w/-> 

V/--2-' 


BY  THE  SAME  AUTHOR. 

Evolution  of  To-Day.— A  Summary  of  the  Theory  of  Evo- 
lution as  held  by  modern  scientists,  and  an  account  of  the 
progress  made  through  the  investigations  and  discussions 
of  a  quarter  of  a  century.  Octavo  .  .  .$175 

CONTENTS:  Introduction  —  What  is  Evolution ?  — Are 
Species  Mutable  ?— Classification  of  the  Organic  World- 
Life  During  the  Geological  Ages— Embryology— Geo- 
graphical Distribution — Darwin's  Explanation  of  Evolu- 
tion— More  Recent  Attempts  to  Explain  Evolution — The 
Evolution  of  Man. 

"  There  have  been  so  many  volumes  upon  evolution  that  an  ordi- 
nary reader  may  be  inclined  to  overlook  this  of  Professor  Conn.  We 
warn  him,  however,  that  in  so  doing  he  is  sure  to  miss  a  rare  contribution. 
It  is  just  the  thing  to  set  a  layman  right  and  is  thoroughly  judicial.  It 
sets  down  the  general  trend  of  thinkers  as  to  evolution  and  Darwinism, 
finding  limits  to  both  and  marking  their  usefulness  when  properly 
employed."— Hartford  Post. 

"  Dr.  Conn  evidently  favors  the  theory,  but  he  does  not  write  as  a 
partisan  or  to  carry  a  point,  but  simply  to  show  what  has  been  the  result 
of  the  fruitful  labors  of  the  last  twenty-five  years.  As  a  devout  theist,  he 
considers  evolution  simply  a  method  of  creation,  and  does  not  believe  that 
this  derogates  from  the  glory  of  the  Divine  Architect." — N.  Y.  Observer. 

G.  P.  PUTNAM'S  SONS,  NEW  ,¥ORK  AND  LONDON. 


EVOLUTION  OF  TO-DAY 


A    SUMMARY 

OF   THE    THEORY  OF   EVOLUTION  AS   HELD  BY  SCIENTISTS 

AT  THE  PRESENT  TIME,  AND  AN  ACCOUNT  OF  THE 

PROGRESS    MADE    BY    THE   DISCUSSIONS 

AND    INVESTIGATIONS   OF 


A  QUARTER  OF  A  CENTURY 


H.  W.  CONN,  PH.D. 

PROFESSOR   OF   BIOLOGY   AT   WESLEYAN   UNIVERSITY 


NEW  YORK  &  LONDON 

G.  P.  PUTNAM'S    SONS 

8^1  luuchtrboclur  |)rtss 

1896 


COPYRIGHT    BY 

G.  P.  PUTNAM'S  SONS 
1886 


Press  of 

G.  P.  PUTNAM'S  SONS 
New  York 


LIBRARY 

UNIVERSITY  OF  CALIFORNIA 
SANTA  BARBARA 


PREFACE. 


MUCH  misunderstanding  exists,  even  in  the  minds 
of  educated  people,  concerning  the  relation  of  the 
thinking  world  to  the  theory  of  evolution.  Com- 
paratively few,  except  those  who  have  made  special 
study  of  the  subject,  are  aware  even  of  the  sort  of 
arguments  which  have  led  scientists  to  accept  evo- 
lution. The  question  is,  however,  too  important  for 
any  educated  person  to  be  satisfied  with  ignorance. 
The  excuse  for  the  present  book  is  to  fill  a  vacancy 
in  our  literature :  to  give  for  those  who  are  inter- 
ested in  the  vital  questions  of  the  age  a  brief  account 
of  this  theory  as  it  stands  to-day  in  the  minds  of 
scientists.  Much  advance  has  been  made  since  the 
time  of  Darwin's  first  writings.  Some  of  his  claims 
have  been  substantiated  and  some  disproved.  His 
own  theory  has  been  examined,  tested,  and  partially 
abandoned,  and  others  have  been  advanced  in  its 
place.  This  book  is  intended  to  indicate  as  nearly 
as  possible  the  foundation  which  the  theory  has 
built  for  itself.  I  shall  therefore  attempt  to  sum- 
marize the  various  lines  of  arguments  advanced  and 
discussed  upon  all  sides  ;  to  enumerate  the  import- 
ant difficulties  which  have  arisen,  together  with  the 


iv  EVOLUTION  OF  TO-DAY. 

evolutionists'  answers  ;  and  briefly  to  consider  the 
most  important  of  the  theories  of  evolution  which 
science  has  produced  ;  to  give,  in  short,  a  summary 
of  the  evolutionary  thoughts  of  the  past  quarter  of 
a  century. 

These  pages  are  intended  for  those  who,  having 
an  interest  in  the  question,  have  neither  the  time 
nor  the  requisite  knowledge  of  biology  to  read  the 
numerous  special  discussions  upon  the  various 
phases  of  the  subject.  The  works  of  Darwin  and 
Spencer  are  too  ponderous  for  any  except  special 
students.  Frequently,  indeed,  their  abundance  of 
detail  somewhat  obscures  the  general  line  of  argu- 
ment. For  this  reason,  readers  who  are  not  scien- 
tists frequently  fail  to  perceive  the  force  of  the 
arguments,  even  after  they  have  carefully  read  the 
books  of  these  authors.  I  shall  therefore  try  to 
free  the  arguments  as  much  as  possible  from  detail, 
only  mentioning  special  cases  for  the  purpose  of 
illustration.  It  will  be  understood  that  the  general- 
ized statements  made  are  supported  by  numerous 
facts,  even  though  in  many  cases  only  the  bare 
statement  is  given. 

The  subject  will  be  treated  as  a  scientific  ques- 
tion, with  only  a  word  here  and  there  regarding  its 
relation  to  other  lines  of  thought.  Evolution,  if 
true,  is  simply  a  law,  and  as  such  should  be  treated 
as  any  other  scientific  law.  It  is  true  that  the  rela- 
tion of  this  question  to  theology,  philosophy,  and 
metaphysics  is  of  the  highest  importance  ;  but  no 
more  so  than  that  of  other  laws.  Science  must  first 
decide  upon  the  existence  of  the  law  and  its  work- 


PREFACE.  V 

ing  in  nature.  If  it  be  found  to  express  a  fact,  other 
lines  of  thought  must  determine  its  significance. 
No  law  is  self-sufficient,  and  evolution  no  more  ex- 
plains itself  than  does  the  law  of  gravitation. 

The  arguments  advanced  in  these  pages  are,  with 
few  exceptions,  such  as  may  be  found  elsewhere  in 
the  various  discussions  upon  the  subject.  I  do  not, 
however,  consider  it  desirable  to  give  authorities, 
since  the  arguments  have  by  this  time  become  the 
common  property  of  the  world.  These  arguments 
I  shall  try  to  state  as  fairly  as  possible  ;  and  when  a 
direct  statement  is  made,  it  may  be  understood  as 
one  which  is  almost,  if  not  universally,  acknowl- 
edged. It  is  of  course  impossible  wholly  to  elimi- 
nate the  factor  of  personal  opinion  ;  but  in  most 
cases  the  conclusions  drawn  are  those  which  have 
been  arrived  at  by  students  in  general,  and  are  not 
the  opinions  of  individuals. 


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TABLE  OF  CONTENTS. 


PAGE 
I 


INTRODUCTION — WHAT  is  EVOLUTION  ?         . 

Original  meaning  of  the  term  in  scientific  literature — Evolu- 
tion and  Darwinism — Evolution  and  theology — Prevalence 
of  the  evolutionary  theory  to-day. 

I. 

ARE  SPECIES  MUTABLE  ?         .        .        .        -* '  '    .       22 
Immutability  of  species — Variation — Causes  of  variation — 
Limits  of  variation — Are  species  stable  ? — Sterility  of  hybrids 
and  fertility  of  mongrels — Indirect  evidence  from  the  rela- 
tions of  animals  ;  From  fossils,  from  reversions — Summary. 

II. 

CLASSIFICATION  OF  THE  ORGANIC  WORLD  .  .  53 
Existence  and  significance  of  a  classification — The  explana- 
tion of  Cuvier — The  explanation  of  evolution — The  relation 
of  species  expressed  by  a  branching  structure — Reasons  for 
this  conclusion — Value  of  the  tree-like  classification — Appli- 
cation of  the  theory  to  the  explanation  of  homology — Ho- 
mology  in  general — Serial  homology — Rudimentary  organs 
— Aborted  organs — Nascent  organs — Summary. 

III. 

LIFE  DURING  THE  GEOLOGICAL  AGES     ...       89 
Significance  of  the  evidence — Imperfection  of  the  record — 
First  appearance  of  life  in  the  Silurian  age — Difficulty  in 
regard  to  time — Absence  of  numerous  generalized  forms  in 


viii  EVOLUTION  OF  TO-DAY. 


the  Silurian — Diversity  of  Silurian  life — Recent  discoveries 
of  connecting  links — Geological  position  of  these  links — De- 
velopment of  the  brain  of  mammals — Paleobotony — Sum- 
mary 

IV. 

EMBRYOLOGY 120 

Importance  of  embryology — Embryology  a  repetition  of 
past  history — (i)  Truth  of  this  assumption,  as  shown  by  com- 
parison of  embryology  with  paleontology  ;  with  a  hypothet- 
ical history  drawn  from  classification — Contradictions  arising 
and  their  explanation — Result  of  previous  considerations — 
Embryology  as  an  assistance  in  classifying  animals.  (2)  Sig- 
nificance of  the  parallel.  (3)  Application  of  the  principle 
— Difficulties  to  be  overcome  in  drawing  a  history  from  em- 
bryology— Abundance  of  hypothetical  stages  necessary — 
Embryological  history  of  animals  in  general — Early  diver- 
gence of  types  from  a  common  point — Summary. 

V. 

GEOGRAPHICAL  DISTRIBUTION  .  .  .  .165 
Complexity  of  the  factors — Animals  not  distributed  accord- 
ing to  climate — Laws  of  distribution  which  should  follow  if 
the  descent  theory  is  true — Relation  of  the  present  to  the 
past — ZoSlogical  regions — Present  distribution  of  species, 
genera,  families,  and  orders — Do  barriers  limit  the  areas  of 
distribution  ?  —  Oceanic  islands  —  Bermudas  —  Galapagos 
islands— St.  Helena— Summary. 

VI. 

DARWIN'S  EXPLANATION  OF  EVOLUTION  .  .  203 
Summary  of  the  evidence— Darwinism— Incompleteness  of 
Darwinism — Difficulties  from  the  slowness  of  the  modifica- 
tion ;  from  the  minuteness  of  changes — Transitional  stages 
wanting — Specific  characters  not  always  useful — Ornamental 
structures — Tendency  toward  elimination  by  crossing — De- 
velopment of  organs  by  small  steps — Similarity  in  indepen- 
dently acquired  organs — Mimicry — Sterile  insects — Sum- 
mary. 


CONTENTS.  IX 

VII. 

PAGE 

MORE  RECENT  ATTEMPTS  TO  EXPLAIN  EVOLUTION  244 
Necessity  of  additions  to  the  theory  of  natural  selection — 
Theory  of  migration  of  Wagner — Internal  factors  in  evolu- 
tion— Tendencies  toward  progression,  Nageli — Extraordinary 
births,  Mivart — Neo-Lamarckianism,  the  American  school 
— Heredity — Brooks'  theory  of  heredity  and  the  cause  of 
simultaneous  variation — Summary. 

VIII. 

THE  EVOLUTION  OF  MAN 288 

Reason  for  a  separate  consideration  of  this  subject — Man's 
physical  nature — Geological  evidence  is  lacking — Man  as  an 
intelligent  animal — Method  by  which  the  evolutionist  ac- 
counts for  man's  great  intellect — Evidence  from  fossils  im- 
possible— Instinct  and  intelligence — Emotions — Knowledge 
of  tools — Language  —  Consciousness  —  Power  of  improve- 
ment— Power  of  abstract  ideas — Various  intuitions — Moral 
nature — Religion,  reverence,  belief  in  immortality — Con- 
science— Darwin's  explanation  of  conscience — Chief  point 
where  this  explanation  fails — Summary — Man  according  to 
all  theories  is  radically  distinct  from  other  animals — General 
summary  and  conclusion. 

INDEX 339 


EVOLUTION  OF  TO-DAY. 


INTRODUCTION. 

IT  is  now  a  full  quarter  of  a  century  since  the  pub- 
lication of  Darwin's  "  Origin  of  Species  "  opened  to 
the  world  a  new  line  of  thought.  Not  only  in 
science  did  this  book  offer  an  untrodden  field  for 
investigation,  but  its  influence  has  extended  to  all 
other  departments  of  learning.  The  general  idea 
of  evolution  which  this  book  brought  into  prominent 
notice  has  invaded  the  domain  of  philosophy,  men- 
tal science,  philology,  and  even  our  conceptions  of 
religion  and  revelation  have  been  modified  by  it. 
Hardly  a  line  of  study  can  be  taken  up  without 
meeting  at  the  outset  this  question  of  origin. 
Whatever  may  be  the  conclusion  as  to  the  truth  of 
the  ideas  embodied  in  this  work  of  Darwin,  no  one 
will  fail  to  recognize  that  they  have  had  an  enor- 
mous influence  upon  the  thought  of  the  age.  We 
read  everywhere  of  evolution,  evolution  of  the  uni- 
verse, of  life,  of  intellect,  of  morals,  of  language  ; 
and  even  artificial  products  are  viewed  under  a  like 
law,  and  the  evolution  of  the  steamboat  or  of  the 
steam-engine  is  not  an  unfamiliar  phrase.  All  this 


2  EVOLUTION  OF  TO-DAY. 

is,  largely  at  least,  the  outcome  of  the  theories  first 
advanced  and  discussed  by  Darwin. 

It  is  impossible  that  twenty-five  years  of  mental 
activity  could  have  passed  without  adding  much  to 
the  evidence  both  in  favor  of  and  against  the  views  of 
Darwin.  Evolution,  using  the  term  in  a  general 
sense,  has  been  applied  to  every  possible  notion  ; 
its  meaning  has  been  expanded  and  contracted ; 
every  realm  of  science  has  been  searched  both  for 
proof  and  disproof  of  the  idea  ;  facts  have  been  col- 
lected from  all  sources  both  relevant  and  irrelevant, 
until  the  amount  of  matter  which  has  been  written 
bearing  upon  some  of  the  numerous  phases  of  the 
question  is  so  great  as  to  make  it  hopeless  for  any 
one  to  attempt  to  fathom  it  all.  The  amount  of 
evidence  which  various  investigators  have  brought 
forward  is  so  great,  and  the  facts  are  so  varied,  that 
no  one  with  the  slightest  bias  of  opinion  has  any 
difficulty  in  finding  arguments  for  almost  any  view. 
This  is  well  shown  by  the  numerous  secondary 
theories  which  have  been  advanced  in  connection 
with  the  general  one,  some  of  which  are  contradic- 
tory, but  all  well  supported  by  facts.  Even  on  the 
general  theory  of  evolution  itself,  so  varied  are  the 
data  collected,  that  neither  friends  nor  foes  have  the 
slightest  difficulty  in  selecting  from  the  large  stores 
of  facts  many  which  support  their  views.  Quite 
frequently  indeed,  the  same  set  of  facts  is  made  to 
serve  on  both  sides,  as  an  argument  for  and  against 
evolution.  If  one  desires  to  do  so  it  is  easy  to  make 
out  a  case  on  either  side.  By  confining  the  atten- 
tion to  favorable  arguments  alone,  evolution  can  be 


INTRODUCTION.  3 

made  to  appear  demonstrated  ;  and  by  considering 
the  difficulties,  alone,  an  opposite  result  may  be 
obtained.  Unfortunately  most  of  our  publications 
take  one  of  these  two  courses,  and  are,  therefore,  in 
a  measure  unsatisfactory.  It  requires  more  exten- 
sive reading  and  more  careful  balancing  of  evidence 
than  most  readers  are  inclined  to  give,  to  perceive 
the  real  force  of  the  arguments. 

What  is  Evolution  ? 

It  is  necessary  at  the  outset  to  inquire  into  the 
meaning  of  the  term  evolution.  So  varied  has  been 
the  discussion,  and  so  numerous  the  senses  in 
which  the  word  is  used,  that  to  say  that  one  accepts 
evolution  conveys  no  adequate  idea,  for  it  may 
mean  much  or  it  may  mean  almost  nothing.  When 
first  used,  the  word  had  a  very  different  significance 
from  that  which  now  is  attached  to  it.  It  was 
believed  by  certain  naturalists  of  the  last  century 
that  there  then  existed  in  the  egg  an  individual  pre- 
cisely like  the  adult,  except  that  it  was  too  small  to 
be  visible.  The  development  of  the  egg  was  simply 
the  growth  of  this  minute  individual,  a  growth  pre- 
cisely similar  to  that  taking  place  in  animals  after 
birth.  This  theory  was  called  evolution.  Very 
soon,  however,  it  was  disproved,  for  a  few  observa- 
tions served  to  show  that  no  such  simple  growth 
took  place.  But  the  word  evolution  was  still  re- 
tained to  apply  to  development  in  general,  and  thus 
for  a  long  time  it  simply  referred  to  the  develop- 
ment of  the  individual  from  the  egg.  But  slowly 
the  word  came  to  be  applied  to  a  different  series  of 


4  EVOLUTION  OF  TO-DA  Y. 

phenomena,  while  it  is  still  occasionally  used  in  its 
earlier  significance.  It  has  come  almost  universally 
to  refer  not  to  the  development  of  the  individual 
from  the  egg,  but  to  the  development  of  the  whole 
existing  order  of  nature  from  the  past.  In  this 
sense,  too,  it  has  a  wide  range.  On  the  one  hand, 
it  may  mean  a  simple  advance  of  one  generation 
over  another  in  any  particular.  Man's  rise  in  intelli- 
gence during  the  last  two  thousand  years  is  said  to 
be  evolution  ;  or  the  gradual  growth  in  the  efficacy 
of  weapons  of  war  may  be  called  an  evolution.  But 
on  the  other  hand,  the  term  has  been  stretched  in  its 
meaning  until  it  covers  the  origin  of  all  things,  and 
with  certain  philosophers  it  is  supposed  to  be  a  uni- 
versal law  which  explains  the  present  universe. 
Foremost  among  these  stand  Spencer  and  Haeckel, 
who  believe  that,  starting  with  the  existence  of  a 
homogeneous  nebular  mass,  the  result  by  the  sim- 
plest natural  laws  would  be  a  system  such  as  we 
now  find.  Spencer  tells  us  that  by  the  unequal 
action  of  force  upon  this  nebula,  its  homogeneity  is 
soon  broken  up,  and  the  nebula  thus  becomes  re- 
solved into  a  number  of  unequal  masses.  By  the 
continued  action  of  the  same  persistent  force,  the 
masses  concentrate,  and  the  planets  appear  with 
their  satellites.  Later,  by  the  same  process,  atoms 
of  carbon  unite  with  atoms  of  hydrogen,  nitrogen, 
and  oxygen,  and  the  result  is  protoplasm  ;  and  thus 
life  arises  spontaneously.  Life  now  goes  on  develop- 
ing, the  old  giving  rise  to  new  and  constantly  higher 
and  more  complex  forms,  until  the  result  is  the 
present  vegetable  and  animal  world,  which  has  thus 


IN  TROD  UCTION.  5 

arisen  by  ordinary  generation.  Finally,  by  the  con- 
tinued development  of  the  nervous  system,  the 
intellect  makes  its  appearance,  rises  higher  and 
higher,  until  it  reaches  the  grade  which  we  find  in 
man.  Evolution  is  here,  then,  a  comprehensive 
theory,  covering  the  slow  growth  of  the  whole  uni- 
verse by  the  simple  action  and  interaction  of  force, 
according  to  natural  law.  But  even  in  this  most 
comprehensive  sense  the  theory  does  not  attempt  to 
explain  the  origin  of  the  universe.  To  start  with,  it 
assumes  the  existence  of  force  and  of  a  homogene- 
ous mass  of  matter. 

Between  the  two  extremes  may  be  found  almost 
every  grade,  for  evolution,  when  defined,  means 
simply  that  the  past  has  given  rise  to  the  present 
by  the  simple  process  of  development  according  to 
natural  law.  But,  although  the  word  may  thus 
mean  almost  any  thing,  and  does  have  different  sig- 
nificance with  different  thinkers,  it  has,  nevertheless, 
in  scientific  literature,  a  tolerably  definite  meaning. 
Among  scientists  the  term  seldom  covers  the 
amount  of  ground  which  is  included  in  Spencer's 
theory,  nor  does  it  ever  stop  at  the  other  meaning- 
less extreme.  As  ordinarily  used  in  most  scientific 
books  to-day,  evolution,  organic  evolution,  and  the 
theory  of  descent  are  practically  synonymous  terms, 
and  each  of  these  is  used  to  indicate  the  theory 
that  all  species  of  animals  and  plants  existing  to-day 
have  been  derived  from  others  living  in  the  past, 
by  direct  descent,  and  that  they  will  themselves 
give  rise  in  the  future  to  other  still  different  species. 
It  further  implies  that  if  the  histories  of  all  animals 


6  EVOLUTION  OF  TO-DAY. 

living  to-day  could  be  traced  backward,  they  would 
all  be  found  to  converge,  until  finally  they  met  at  a 
common  point  of  union,  which  would  represent  a 
common  ancestor  living  in  the  remote  past.  In 
short,  evolution,  as  the  term  is  commonly  under- 
stood to-day,  is  chiefly  a  denial  of  the  former  belief 
that  species  were  independently  created,  and  the 
replacement  of  this  belief  with  its  opposite.  It  as- 
sumes that  no  species  is  an  independent  creation, 
but  that  all  are  derived  from  past  forms  now  mostly 
extinct.  This  is  evolution  as  Danvin  understood  it ; 
this  is  the  common  understanding  of  the  term  to- 
day in  scientific  literature  ;  and  this  is  the  question 
which  has  been  so  thoronghly  investigated  in  the 
last  twenty-five  years. 

As  thus  defined,  it  is  easy  to  see  that  the  theory 
is  not  complete,  since  nothing  is  said  as  to  the 
origin  of  life.  The  essential  idea  which  underlies 
the  whole  theory  is  that  species  have  had  a  natural 
rather  than  a  supernatural  origin ;  and  it  is  evident 
that  unless  we  give  a  natural  explanation  of  the 
origin  of  life,  the  idea  is  lacking  at  its  very  founda- 
tion. Nor  is  this  all ;  for  the  same  logical  necessity 
will  compel  us  to  explain,  in  a  similar  way,  the  ori- 
gin of  the  world  and  the  solar  system,  and  thus  to 
reach  a  theory  something  like  that  of  Spencer.  But 
even  this  theory  does  not  reach  any  bottom,  for  it 
assumes  the  existence  of  the  nebula,  and  Spencer 
found  it  necessary  to  put  behind  and  beneath  his 
system  an  "  unknowable,"  which  he  considered  the 
same  as  the  God  of  theology.  It  is  therefore  im- 
possible to  make  evolution  a  complete  theory. 


INTRODUCTION.  7 

Since,  then,  this  is  a  logical  impossibility,  it  is  best 
to  admit  the  fact  and  confine  our  conception  of 
evolution  to  the  realm  where  there  is  evidence  for  it. 
Now,  at  the  beginning  of  life  there  is  a  break  in  the 
series.  There  is  not  yet  the  slightest  evidence  that 
living  matter  could  arise  from  non-living  matter. 
All  of  the  most  recent  experiments  have  certified 
this  conclusion.  Scientists,  perceiving  it  a  logical 
necessity  of  these  views  to  believe  that  life  could 
have  arisen  from  inorganic  matter,  have  had  natu- 
rally a  great  desire  to  prove  this  possibility.  The 
fact  that  spontaneous  generation  is  universally  given 
up  is  therefore  a  testimony  to  the  cogency  of 
the  conclusion  and  the  honesty  of  the  investiga- 
tors. But  on  the  other  hand,  it  is  evident  enough 
that  while  the  experiments  of  Tyndall  and  others 
prove  that  life  cannot  arises:  pontaneously  in  the 
conditions  under  which  they  have  performed  their 
experiments — /.  e.,  in  closed  flasks  containing  boiled 
solutions,  they  by  no  means  prove  that  spontaneous 
generation  could  not  have  taken  place  under  other 
different  circumstances.  We  can  know  nothing  as 
to  what  may  have  taken  place  under  different  con- 
ditions. It  is  equally  possible  for  one  side  to  claim 
that  the  experiments  teach  that  life  cannot  arise 
spontaneously,  and  for  the  other  side  to  claim  that 
while  it  does  not  do  so  now,  it  might  have  been 
possible  under  very  different  circumstances  in  times 
past.  In  short,  the  question  is  not  open  to  investi- 
gation. It  is  impossible  to  prove  that  spontaneous 
generation  could  never  have  occurred ;  and  it  is 
extremely  improbable  that  the  opposite  view  will 


8  EVOLUTION  OF  TO-DAY. 

ever  be  demonstrated.  All  that  can  be  done  is  to 
discuss  the  question  from  theoretical  grounds. 
There  is  then  a  break  at  the  beginning  of  life,  since 
spontaneous  generation  can  be  neither  proved  nor 
disproved.  This  fact  makes  it  far  preferable  for  the 
present  at  least  to  confine  the  term  evolution,  in  our 
ordinary  discussion,  as  Darwin  did,  to  the  develop- 
ment of  life,  without  including  any  theory  as  to  its 
origin  ;  realizing  all  the  while  that  as  thus  stated 
the  theory  is  not  complete.  If  we  do  confine  the 
term  to  these  limits  we  have  a  theory  which  is  open 
to  investigation,  and  which  may  some  time  be  ap- 
proximately demonstrated.  But  if  we  attempt  to 
include  all  that  Spencer  understands  by  the  term, 
there  is  little  hope  that  we  can  advance  beyond 
hypothesis.  Scientists,  therefore,  as  a  rule,  restrict 
the  term  to  the  development  of  living  organisms. 
It  is  the  object  of  the  following  pages  to  discuss  the 
question  in  this  sense,  as  a  scientific  theory,  there- 
fore, without  reference  to  the  deeper  metaphysical 
problems  underlying  the  more  comprehensive  signi- 
ficance of  evolution  as  applied  to  the  origin  of  the 
universe.  Whenever  the  term  evolution  is  used  in 
the  following  pages,  it  is  in  the  sense  above  indicated, 
and  is  synonymous  with  the  terms  organic  evolution 
and  the  theory  of  descent. 

Are  there  any  other  breaks  in  the  chain  of  con- 
tinuity which  may  make  it  wise  to  limit  still  further 
the  meaning  of  evolution  ?  It  is  claimed  by  many 
that  such  a  break  is  found  in  man  ;  not  so  far  as  his 
body  is  concerned,  but  because  he  represents  a  new 
order,  in  intellect  and  morality.  This  question  is 


INTRODUCTION.  9 

reserved  for  a  separate  chapter.  But  more  than  this, 
it  has  been  held  by  certain  naturalists  that  species 
have  arisen  from  several  distinct  points,  and  not 
from  one.  They  would  say  that  there  have  been  a 
number  of  points  of  origin,  one  for  each  of  the  sub- 
kingdoms.  But  this  position  is  hardly  a  tenable 
one  and  is  now  generally  abandoned.  It  is,  of 
course,  perfectly  possible  that  such  might  have  been 
the  history  of  animals,  even  upon  the  theory  of 
evolution,  but  there  is  not  the  slightest  evidence 
that  such  was  the  case.  On  the  contrary,  as  we 
shall  see  later,  the  evidence  is  such  as  to  apply  to  all 
species  alike,  and  if  its  force  is  admitted  at  all,  it 
must  be  admitted  as  linking  the  organic  world  into  a 
single  unit,  and  not  into  several.  The  sub-kingdoms 
are  united  together  at  the  bottom,  and  if  evolution 
is  admitted  at  all,  it  must  apply  to  the  whole  organic 
world.  While,  then,  it  is  desirable  to  confine  the 
subject  to  limits  where  it  can  be  investigated  and 
attested  by  facts,  it  is  equally  desirable  to  avoid  the 
other  extreme  and  fail  to  see  that  evolution  must 
cover  all  organic  species  or  none. 

Evolution  is  not  Darwinism. 

We  have  now  reached  a  conclusion  as  to  what  is 
ordinarily  meant  by  evolution,  and  such  was  Dar- 
win's understanding  of  the  term.  But  it  must  not 
be  confounded  with  Darwinism.  Evolution  is  sim- 
ply a  theory  as  to  the  method  by  which  species  have 
been  introduced  into  the  world,  entirely  independent 
of  any  idea  as  to  the  causes  which  have  brought  about 
their  introduction.  Darwinism  is  evolution  ;  but  it 


10  EVOLUTION  OF  TO-DAY. 

is  more  than  this  ;  it  is  at  the  same  time  an  attempt 
at  an  explanation  of  the  causes  of  evolution.  It 
not  only  claims  that  species  have  been  slowly 
evolved  from  each  other,  but  it  also  gives  an  ac- 
count of  the  manner  in  which  they  have  arisen,  and 
the  laws  which  govern  their  gradual  modification. 
It  is,  therefore,  possible  to  accept  evolution  and  to 
reject  Darwinism  completely  ;  to  believe  that  species 
have  been  evolved  from  each  other,  but  to  deny  that 
Darwin  has  discovered  the  causes  of  this  evolution. 
And  so  with  various  other  theories  of  evolution, 
of  which  science  has  proposed  several.  All  agree 
as  to  the  evolution  of  species  from  each  other,  but 
no  two  explain  the  fact  in  the  same  manner.  For 
we  must  recognize  two  quite  different  questions  in 
considering  the  subject.  The  first  is  as  to  the  fact 
of  evolution.  We  must  discover,  if  possible  what 
has  been  the  history  of  organisms  ;  whether  each 
species  is  to  be  considered  as  an  abrupt  innovation, 
utterly  independent  of  all  others — i.  t.,  a  special 
creation,  or  whether  species  have  been  derived  from 
each  other  by  the  ordinary  methods  of  reproduction 
aud  slow  change.  If  it  is  discovered  that  the  evi- 
dence is  sufficient  to  prove  evolution  to  be  a  fact, 
or  to  render  it  probable,  a  second  and  more  difficult 
question  remains.  We  must  discover  what  are  the 
laws  which  regulate  this  evolution,  and  must  deter- 
mine how  species  have  been  derived  from  each  other, 
whether  slowly  or  abruptly,  whether  by  internal  or 
external  forces,  and  other  problems  of  like  nature. 
In  reality  these  two  questions  have  been  considered 
simultaneously,  all  theories  of  evolution  attempting 


INTRODUCTION.  II 

to  answer  both  questions;  or  more  frequently  they 
assume  evolution  and  attempt  simply  to  find  an  ex- 
planation of  the  fact. 

In  the  following  pages  these  two  questions  will 
be  considered  separately  as  far  as  possible,  though 
they  are  so  intimately  connected  as  to  make  a  com- 
plete separation  impossible.  In  the  first  five  chap- 
ters we  shall  discuss  the  question  whether  evolution 
be  a  fact.  Here  we  shall  consider  the  various  argu- 
ments which  have  been  adduced  to  prove  that  species 
have  been  derived  from  each  other,  and  the  various 
difficulties  and  objections  which  have  arisen  against 
the  unhesitating  acceptance  of  this  view.  In  the 
sixth  and  seventh  chapters  we  will  examine  the  sev- 
eral theories  of  evolution  held  by  different  scientists, 
which  attempt  to  explain  the  fundamental  fact,  and 
to  give  the  causes  which  have  produced  the  devel- 
opment of  new  species. 

Darwinism  proper  is,  then,  not  evolution,  but  its 
explanation.  Darwin's  contribution  to  science  was 
his  law  of  natural  selection,  a  principle  which  he  be- 
lieved to  be  the  chief  cause  of  the  development  of 
new  species.  Darwin  did  not  originate  the  theory 
of  evolution,  although  it  is  rightly  associated  with 
his  name.  If  the  writings  of  Descartes,  Leibnitz, 
and  Goethe  be  carefully  studied,  the  beginnings  of 
the  modern  ideas  involved  in  the  term  can  be  traced. 
Very  indefinite  they  were,  it  is  true,  and  so  they 
remained  until  about  the  beginning  of  the  present 
century.  At  this  time  a  French  naturalist,  Lamarck, 
formulated  a  logical  and  consistent  theory  of  evolu- 
tion, a  theory  which  agreed  in  almost  all  respects 


12  EVOLUTION  OF  TO-DAY. 

with  the  one  that  is  still  held  at  the  present  day  by 
many  American  naturalists.  He  not  only  believed 
in  the  origin  of  species  from  each  other,  but  he  gave 
an  explanation  of  his  theory.  And  the  explanation 
which  he  gave  is  accepted  to-day  by  many  natural- 
ists as  being  nearer  to  the  truth  than  that  of  Darwin. 
But  Lamarck  was  ahead  of  his  age,  and  the  world 
was  not  ready  for  his  views.  He  had,  moreover,  the 
great  authority  of  Cuvier  against  him,  and  the 
weight  of  Cuvier's  name  soon  caused  Lamarck  and 
his  evolution  to  sink  into  oblivion,  to  reappear  oc- 
casionally at  fitful  periods  as  the  next  half  century 
passed.  In  1859  the  publication  of  Darwin's  "  Ori- 
gin of  Species  "  brought  the  old  view  once  more  into 
prominence  under  a  new  light.  For  twenty  years 
Darwin  had  been  patiently  investigating  the  theory 
before  he  published  a  word,  and  when  he  did  appeal 
to  the  world  he  not  only  could  give  very  strong 
arguments  for  accepting  the  general  theory  of  evo- 
lution, but  he  offered  at  the  same  time  an  extremely 
simple  and  comprehensive  explanation.  A  consid- 
eration of  this  explanation  we  must  defer  ;  but  so 
strong  were  Darwin's  arguments,  and  so  skilfully 
were  they  handled,  that  the  scientific  world  began 
immediately  to  discuss  the  question.  Not  a  little 
of  Darwin's  influence  was  due  to  the  great  candor 
of  his  discussion  and  the  readiness  with  which  he 
acknowledged  the  difficulties  which  he  could  not 
meet.  From  that  time  evolution  has  been  con- 
stantly before  the  world.  Not  only  has  much  evi- 
dence been  collected  in  the  endeavor  to  prove  or 
disprove  evolution,  but  the  explanation  offered  by 


INTRODUCTION.  13 

Darwin  has  been  subjected  to  thorough  examina- 
tion. It  has  been  carefully  applied  to  all  sorts  of 
facts  ;  its  weak  points  and  strong  points  have  been 
discovered  ;  and  new  theories  have  been  suggested 
in  its  place.  The  prominence  of  this  question  in 
modern  times  is  therefore  due  to  the  influence  of 
Darwin,  and  his  name  will  always  be  associated  with 
it,  even  though  he  was  not  the  originator  of  the 
theory  of  evolution,  and  though  his  own  explanation 
of  the  theory  should  be  largely  abandoned. 

Evolution  and  Theology. 

From  the  very  first,  evolution  has  been  obliged  to 
contend  with  prejudices  arising  partly  from  igno- 
rance of  the  theory  and  partly  from  the  natural 
tendency  to  cherish  old  ideas.  The  current  conflict 
of  science  and  religion  has  at  times  been  vigorous 
over  this  question.  Scientists,  by  this  theory,  offered 
to  remove  a  whole  series  of  miraculous  events  from 
nature.  Species,  which  were  before  looked  upon  as 
the  direct  handiwork  of  God,  were  now  regarded  as 
the  results  of  natural  law.  Evolution  was  supposed 
to  be  in  contradiction  to  revelation,  which  had  al- 
ways been  supposed  to  teach  the  special  creation  of 
species.  Atheistic  scientists  claimed  to  have  aimed 
a  heavy  blow  at  theism  by  this  theory,  and  the  the- 
ists  quite  naturally  attempted  to  destroy  the  weapon 
before  the  blow  reached  them.  The  weapon  has 
not  been  destroyed,  but  it  has  been  found  to  be 
harmless,  for  theism  stands  unmoved  by  evolution- 
ary theories. 

The  arguments  which  have  been  most  potent  in 


14  EVOLUTION   OF  TO-DAY. 

causing  a  rejection  of  evolution  have  frequently 
been  of  no  scientific  importance.  Instead  of  trying 
to  find  out  whether  evolution  is  true,  many  begin  at 
the  other  end.  They  select  certain  unpleasant  re- 
sults which  they  say  will  follow  if  the  theory  be 
true,  and  then  proceeding  to  show  that  these  results 
cannot  be  accepted,  assume  to  have  disproved  the 
theory.  One  voluminous  book,  published  within  a 
year,  assumes  to  start  with,  that  if  evolution  were 
true  Christianity  would  be  overthrown,  and  with 
this  as  a  foundation  proceeds  to  demolish  the  the- 
ory. But  such  reasoning  is  worse  than  worthless  ;  it 
is  a  positive  injury  both  to  science  and  religion,  be- 
cause it  gives  a  false  idea  of  both.  Christianity 
does  not  want  such  defence,  nor  does  science  care  in 
the  least  for  such  attacks.  The  truth  of  the  theory 
of  evolution  must  be  decided  by  the  evidence 
which  can  be  adduced,  and  not  by  the  results  which 
we  may  think  would  follow. 

Hugh  Miller  used  to  say  that  it  was  the  misfor- 
tune of  theology  to  be  fifty  years  behind  science. 
As  soon  as  scienpe  advances  any  theory,  theology 
thinks  to  discover  it  to  be  contrary  to  revelation, 
and  immediately  attempts  to  prove  this  contradic- 
tion. After  much  time  is  spent  in  such  discussion 
the  discovery  is  made  that  science  has  in  the  mean- 
time demonstrated  the  theory  in  question.  Theol- 
ogy is  then  obliged  to  retrace  its  steps  ;  and  usually 
discovers  very  soon  that  its  earlier  interpretations 
were  erroneous.  This  has  been  the  history  of  al- 
most all  scientific  theories,  and  thus  according  to 
Hugh  Miller  theology  is  fifty  years  behind  science. 


IN  TROD  UCTION.  1 5 

Fortunate  enough  perhaps  it  is,  for  this  fact  pre- 
vents a  too  precipitous  advance,  and  compels  sci- 
ence to  give  good  reasons  for  every  step  it  takes. 

In  regard  to  evolution,  however,  it  has  not  re- 
quired fifty  years  to  show  that  a  belief  in  religion  is 
not  materially  affected  by  its  acceptance.  Al- 
ready our  leading  thinkers  among  theologians,  as 
well  as  elsewhere,  have  recognized  that  the  question 
is  a  scientific  one  purely,  and  must  be  decided  upon 
scientific  grounds ;  whether  it  is  decided  in  the 
affirmative  or  the  negative  it  does  not  trouble  the 
belief  in  theism.  Some  people  appear  to  think  that 
to  explain  any  phenomena  by  law,  is  to  take  it  out 
of  the  hands  of  the  Creator ;  and  hence,  if  all 
things  could  be  reduced  to  law,  there  would  be  no 
longer  any  need  for  a  Creator.  But  this  is  plainly 
far  from  the  truth.  Even  if  evolution  be  admitted 
to  its  fullest  extent,  it  does  not  explain  creation  ;  it 
only  proves  continuity.  Darwinism  itself  explains 
the  origin  of  nothing.  It  simply  claims  that  the 
universal  survival  of  the  fittest  varieties  would 
slowly  give  rise  to  new  species.  And  even  the 
other  theories  which  attempt  to  account  for  these 
varieties  do  not  touch  any  bottom,  although  they 
go  deeper  into  the  matter.  It  is  an  old  saying,  that 
evolution  cannot  exceed  involution  ;  a  saying  which 
is  sometimes  held  up  to  ridicule.  But  in  its  true 
sense  it  expresses  an  undoubted  truth.  Evolution, 
using  the  term  now  as  Spencer  uses  it,  does  not 
create,  it  only  modifies.  Were  it  not  true  that  un- 
der all  nature  there  existed  harmonious  laws ;  were 
it  not  true  that  matter  possessed  certain  properties; 


1 6  EVOLUTION  OF  TO-DAY. 

were  it  not  true  that  these  laws  and  properties  were 
such  that  certain  results  could  come  from  the  intro- 
duction of  matter  and  force,  no  evolution  would  be 
possible.  In  this  sense,  then,  evolution  cannot  ex- 
ceed involution.  Evolution  does  not,  in  any  form, 
attempt  to  deal  with  the  question  of  the  origin  of 
matter,  law,  and  force,  but  simply  to  show  that, 
assuming  the  universe  to  have  been  such-and-such 
at  the  start,  its  subsequent  history  has  been  one  of 
continuous  growth.  Once  given  matter  and  force 
and  the  laws  regulating  their  interaction,  and  evo- 
lution claims  that  it  is  unnecessary  to  assume  the 
addition  of  any  thing  more  to  explain  the  existing 
order  of  nature.  To  pretend  that  such  a  view  is  op- 
posed to  the  better  conception  of  theology  is  absurd. 
Evolution,  if  accepted,  does  remove  many  miracles 
from  nature.  But  this  is  not  to  be  regretted.  To 
think  of  God  as  working  by  law  is  a  conception 
vastly  superior  to  the  thought  of  his  working  by 
miracle.  Even  the  most  extreme  evolutionist  finds 
it  necessary  to  assume  the  existence  of  something 
behind  matter  and  force  as  its  foundation,  and  a 
belief  in  evolution  is  only  the  conception  of  this 
power  acting  constantly  and  in  an  orderly  manner. 
Some  people  would  seem  to  think  that  evolution 
either  denies  the  existence  of  God,  or  assumes  that 
His  only  direct  contact  with  the  world  was  at  the 
creation,  and  perhaps  again  at  the  appearance  of 
life ;  and,  except  at  these  two  periods,  he  has  left 
his  creatures  to  themselves.  But  while  it  is  true  that 
some  evolutionists  deny  the  existence  of  a  God,  it 
is  also  true  that  the  latter  view  is  seldom  conceived 


IN  TROD  UCTION.  1 7 

of.  There  is  such  a  belief  as  theistic  evolution  ;  and 
this  belief  would  look  at  all  nature  as  the  continued 
manifestation  of  God.  The  power  of  the  universe  is 
just  as  truly  manifested  in  the  birth  of  an  individual 
as  in  the  creation  of  a  world.  Naturalists  have  not 
succeeded  in  explaining  life,  but  have,  in  evolution, 
discovered  a  new  law  regulating  life.  Instead  of 
being  sufficient  in  itself,  evolution  finds  it  necessary 
to  assume  the  constant  action  of  power  underneath 
nature.  Instead  of  excluding  God  from  nature, 
theistic  evolution  finds  him  as  its  eternal  expla- 
nation. 

It  is  not  our  purpose  here  to  discuss  the  relation 
of  evolution  and  revelation.  The  question  has  been 
much  studied,  and  the  rapidly  growing  opinion 
among  theologians  is  that,  considering  evolution 
as  a  method  of  creation,  it  is  not  at  all  out  of 
harmony  with  the  teachings  of  revelation.  There 
are  certainly  some  views  of  evolution  which  would 
be  fatal  to  any  religious  belief,  but  this  is  not 
because  of  any  principle  necessarily  implied  in  the 
theory.  Neither  natural  theology  nor  revelation 
finds  any  difficulty  in  accepting  the  theory.  Grad- 
ually the  conviction  has  been  growing  on  all 
sides  that  this  subject  is  purely  scientific  and  not 
theological ;  that  it  must  be  decided  by  scientific 
investigators  upon  scientific  evidence.  The  appli- 
cations of  evolution  to  other  realms  besides  the 
organic  world  are  interesting  and  valuable,  but  they 
will  not  aid  toward  settling  the  question  at  issue. 
Almost  everywhere  we  find  a  readiness  to  leave  the 
question  for  scientists  to  settle ;  at  least  to  permit 


1 8  EVOLUTION  OF  TO-DAY. 

them  to  settle  the  method  of  the  origin  of  species, 
although  mental  philosophy,  metaphysics,  theology, 
etc.,  may  still  dispute  with  science  as  to  the  inter- 
pretation  and  significance  of  the  laws  discovered. 
Evolution  is  held  by  Dana,  a  Congregationalist ; 
Lecont,  a  Presbyterian  ;  McCosh,  the  President  of  a 
Presbyterian  college ;  Asa  Gray,  an  Episcopalian ; 
Mivart,  a  Roman  Catholic;  Winchell,  a  Methodist  ; 
Wallace,  a  Christian  spiritualist;  by  the  Bishop  of 
London,  and  by  hosts  of  others,  ministers  and  lay- 
men, whose  names  are  enough  to  indicate  that  it  is 
no  longer  considered  a  heresy  to  accept  evolution ; 
and  that  the  best  thinkers  recognize  the  fact  that 
evolution  produces  no  discord  when  compared  with 
revelation.  So  far,  then,  as  concerns  the  relation  of 
evolution  to  our  ideas  of  Christianity,  we  may  ex- 
amine the  evidence  for  and  against  the  theory  with 
no  prejudice,  and  with  perfect  equanimity  as  to  the 
results. 

Prevalence  of  the  Evolutionary  Theory. 

It  may  be  well  to  say  at  the  outset  that  evolu- 
tion, as  we  have  defined  the  term,  is  almost  uni- 
versally accepted  by  scientists.  A  very  few — they 
can  be  counted  on  the  fingers  of  one  hand — are  still 
inclined  to  withhold  their  acceptance.  These  are 
chiefly  the  older  scientists,  who  had  their  views 
formulated  before  Darwin  wrote,  and  their  number 
is  growing  less.  But  with  these  few  exceptions, 
scientists  are  so  firmly  convinced  of  the  truth  of 
evolution,  that  it  is  always  assumed  as  a  fact,  and 
no  more  time  is  spent  in  discussing  it.  We  find 


INTRODUCTION.  19 

investigations  constantly  carried  on  which  add  data 
to  the  question  tacitly  assumed.  We  find  many 
discussions  as  to  which  of  the  various  theories  of 
evolution  is  the  nearest  the  truth ;  but  it  is  very 
seldom  we  find  in  scientific  literature  any  discussion 
as  to  the  truth  of  the  theory.  Indeed,  the  study  of 
biology  to-day  assumes  evolution  as  its  foundation. 
Whether  a  right  or  wrong  method  of  study,  it  has 
proved  to  be  a  necessity,  and  will  at  all  events 
serve  to  indicate  how  firmly  the  theory  has  become 
rooted  in  modern  science.  Unless  there  is  a  marked 
change  in  the  tendency  of  thought,  it  is  a  safe  pre- 
diction that  a  few  years  more  will  see  it  a  universal 
conclusion  of  science.  The  question  is,  however, 
still  open  to  investigation,  and,  as  we  shall  see, 
there  are  still  many  difficulties  which  have  not  been 
cleared  away.  There  are  still  obstacles  to  be  over- 
come before  the  theory  can  be  regarded  as  positively 
settled. 

Among  students  of  mental  science,  the  term 
evolution  seldom  has  the  same  meaning  that  has 
been  indicated  above.  Their  whole  line  of  thought 
is  different,  and  they  cannot,  therefore,  consider  the 
question  as  a  purely  scientific  subject.  In  their 
minds,  evolution  has  more  meaning  than  it  has 
among  natural  scientists.  It  is  frequently  made  to 
include  certain  metaphysical  conceptions  of  the 
meaning  of  the  individual  life ;  the  significance  of 
reproduction  in  general,  as  well  as  of  the  origin  of 
matter  and  force ;  all  questions  of  the  greatest  sig- 
nificance, and,  perhaps,  rightly  included  in  a  philo- 
sophical definition  of  evolution.  But  these  ideas 


20  EVOLUTION  OF  TO-DAY. 

do  not  form  part  of  the  theory  which  scientists  hold 
and  claim  to  have  approximately  demonstrated. 
For  this  reason,  then,  we  find  various  verdicts  upon 
the  question  from  students  of  mental  science  ; 
though  here,  too,  there  is  a  growing  tendency  tow- 
ard a  belief  in  some  sort  of  evolution. 

Among  theologians,  while  there  are  still  some 
who  oppose  evolution  on  the  ground  that  it  is  con- 
trary to  revelation,  the  number  of  those  who  con- 
cede it  to  be  a  purely  scientific  theory  is  a  growing 
one.  The  willingness  to  accept  the  conclusions  of 
science  upon  this  question  of  fact  is  becoming  more 
and  more  prevalent. 

While,  then,  there  is  some  unanimity  as  to  the  fact 
of  an  evolution,  the  unanimity  goes  no  farther. 
When  the  attempt  is  made  to  explain  the  theory,  or 
to  discover  the  laws  regulating  it,  or  to  discover  its 
limits,  if  such  exist,  or  when  the  theory  is  applied 
to  mental  or  moral  science,  all  agreement  disappears. 
Each  thinker  has  his  own  view.  Darwin  explained 
evolution  by  natural  selection,  while  others  deny  to 
this  explanation  more  than  a  secondary  position. 
Some  would  say  that  there  has  been  a  continual 
slow  progress;  others,  that  there  have  been  alternat- 
ing periods  of  rest  and  rapid  progress ;  some  would 
say  that  new  species  may  arise  in  the  course  of  a 
single  generation,  or,  at  most,  a  few  generations; 
while  others  make  the  production  of  a  new  species  a 
matter  of  many  centuries ;  some  find  the  regulating 
factors  in  the  organism ;  others  in  the  conditions 
surrounding  it.  Some  confine  the  law  to  the  lower 
animals,  and  say  that  it  does  not  apply  to  man; 


INTROD  UCTION. 


21 


some  would  include  man's  physical,  but  not  his 
mental,  nature ;  while  others  believe  that  man  has 
been  wholly  derived  from  the  lower  animals.  To 
these  views  we  shall  again  refer ;  but  it  is  first 
necessary  to  examine  the  evidence  for  evolution, 
exclusive  of  any  of  these  special  theories. 


CHAPTER  I. 

ARE    SPECIES    MUTABLE? 

THE  subject  around  which  the  question  of  evolu- 
tion is  centred  is  the  immutability  of  species.  Are 
species  so  stable  that  they  always  produce  offspring 
like  themselves,  or  can  they  change  so  as  to  give 
rise  either  slowly  or  rapidly  to  new  ones?  If  evolu- 
tion is  a  fact,  the  latter  must,  of  course,  be  true. 
Most  naturalists  claim  that  the  evidence  accumu- 
lated is  sufficient  to  establish  beyond  a  reasonable 
doubt  the  fact  that  species  are  mutable.  They  look 
upon  those  living  to-day  as  descended  from  past 
species,  from  which  they  differ ;  and  as  continually 
changing,  so  that  they  will,  in  turn,  give  rise  to  new 
species  in  the  future.  Indeed,  the  term  species  is 
considered  as  having  no  real  significance,  but  as 
simply  a  convenient  method  of  classing  similar  or- 
ganisms together.  If  this  be  admitted,  the  whole 
problem  of  organic  evolution  is  in  reality  conceded  ; 
for  when  once  it  is  recognized  that  species  are 
derived  from  each  other  by  descent,  the  method  of 
this  derivation,  and  the  number  of  originally  created 
forms,  are  simply  matters  of  detail.  But  this  posi- 
tion is  not  everywhere  conceded,  for  it  is  still  claimed 
by  a  few  that  the  evidence  is  not  sufficient  to  war- 

22 


VARIA  TION.  23 

rant  the  conclusion  of  the  mutability  of  species. 
While,  then,  most  naturalists  regard  the  mutability  of 
species  as  no  longer  questionable,  it  is  a  conclusion 
which  has  not  been  definitely  proved. 

It  will  be  admitted  at  the  outset,  on  all  sides,  that 
no  unquestionable  instance  has  been  observed  of  one 
species  being  derived  from  another.  This  is  not 
surprising,  even  if  the  mutability  of  species  be 
granted.  It  has  been  only  twenty-five  years  since 
naturalists  have  perceived  the  importance  of  the 
question,  and  this  is  far  too  short  a  time  for  changes 
of  importance  to  occur.  But  there  is  even  a  greater 
difficulty  than  this.  Whenever  it  is  shown  that  one 
form  has  given  rise  to  another,  it  is,  of  course,  a  very 
simple  matter  to  say  that  they  are  simply  two  forms 
of  the  same  species.  It  is,  therefore,  impossible  at 
present  to  place  the  matter  beyond  question.  Two 
very  distinct  animals  are  studied,  which  are  every- 
where acknowledged  to  be  distinct  species.  After 
careful  study  and  experiment,  it  is  found  that  one 
may  be  converted  into  the  other,  and  from  this  time 
these  two  species  are  regarded  simply  as  different 
forms  of  one  and  the  same  species;  and  thus  the 
whole  force  of  the  proof  is  lost  by  this  circular 
argument. 

Variation. 

That  species  are  absolutely  immutable  no  one  will 
pretend  to  claim.  It  is  repeatedly  proved  by  facts 
of  every-day  observation  that  species  are  subject  to 
a  certain  amount  of  variation  and  change.  Every 
one  is  aware  of  the  effect  of  food,  climate,  hardship 


24  EVOLUTION  OF  TO-DAY. 

and  ease  upon  animals.  No  child  is  precisely  like 
its  parents.  The  man  of  the  nineteenth  century 
is  very  different  from  the  man  of  2000  B.  C.  The 
European  is  very  unlike  the  African.  Variations 
do  occur,  then,  and  may  (by  being  transmitted  from 
generation  to  generation)  give  rise  to  races.  Among 
animals  and  plants  it  is  everywhere  recognized  that 
there  are  species  and  varieties,  and  all  of  the  varie- 
ties of  a  species  are  understood  as  having  descended 
from  the  same  ancestor.  Indeed,  the  commonly 
recognized  distinction  between  species  and  varieties 
has  been,  until  evolution  modified  it,  that  varieties 
are  descended  from  the  same  parent,  while  species 
are  not  thus  genetically  related.  Nor  will  any  one 
attempt  to  deny  that  the  variations  which  may  thus 
arise  may  be  very  great,  equalling,  or  sometimes  even 
exceeding,  the  amount  of  difference  between  species. 
Compare  the  English  dray-horse  with  the  racer,  the^ 
short-horned  with  the  long-horned  cattle,  the  do- 
mestic hog  with  the  wild  boar — remembering  all  the 
time  that  we  have  here  simple  varieties.  The  vari- 
ous breeds  of  domestic  pigeons  differ  among  them- 
selves so  much  that,  if  found  in  a  state  of  nature, 
they  would  be  ranked  as  different  species,  as  differ- 
ent genera,  or  in  some  cases  as  different  families,  so 
great  is  the  difference  between  them.  The  fan-tail 
has  more  tail  feathers  than  any  other  known  bird, 
and  this  is  a  tolerably  constant  feature  among  birds. 
The  swollen  crop  of  the  pouter  pigeon  is  absolutely 
unique,  and  yet  all  breeds  of  pigeons  are  simple 
variations,  and  no  one  is  inclined  to  deny  that  they 
are  derived  from  the  same  ancient  common  ancestor. 


VARIATION.  25 

In  such  cases  as  these  the  common  origin  of 
the  varieties  is  frequently  a  matter  of  observation. 
But  the  same  sort  of  varieties  occurs  in  a  wild  state, 
although  here  it  is  seldom  possible  directly  to  ob- 
serve their  common  origin.  It  is  probable  also  that 
they  are  not  so  numerous  or  so  great  as  in  the  case 
of  domestic  animals.  Domestic  animals  are  under 
such  abnormal  conditions,  they  are  so  free  from  the 
struggle  for  existence,  so  frequently  manipulated 
by  the  breeder,  as  to  make  them  very  much  more 
liable  to  variation  than  are  wild  species.  Our  breeders 
can,  by  careful  selection,  produce  changes  much  more 
rapidly  than  would  take  place  naturally.  All  of  this 
is  of  course  absent  in  animals  under  nature,  and  the 
variation  will  consequently  be  rather  less  numerous. 
That  animals  in  a  state  of  nature  do  vary  is,  how- 
ever, well  known.  Individual  differences  are  every- 
where found,  for  no  two  animals  are  alike.  Nor  are 
these  variations  confined  to  isolated  individuals. 
They  are  inherited  and  transmitted.  Changes  in 
the  environment  produce  very  great  effect  upon  or- 
ganisms, changes  which  gradually  increase  by  inheri- 
tance. Changes  in  food  affect  the  color  of  animals, 
changes  in  temperature,  climate,  moisture,  or  dry- 
ness,  winds, — all  have  been  found  to  produce  marked 
effects  upon  organisms.  Some  rats  escaping  from  a 
ship  upon  the  island  of  Formosa  became  wild,  and  in 
a  very  few  generations  had  become  so  much  modi- 
fied as  to  be  no  longer  recognizable  as  European 
species.  Allen  has  shown  that  variations  in  latitude 
produce  in  American  birds  changes  in  color,  length 
of  bill,  claws,  and  tails,  while  variations  in  longitude 


26  EVOLUTION  OF  TO-DA  Y. 

only  produce  changes  in  color.  Hardly  a  species  of 
animals  exists  which  does  not  have  two  or  more 
well-marked  varieties,  sometimes  referable  to  differ- 
ences in  conditions,  but  more  frequently  not,  since 
they  may  exist  side  by  side.  Now  since  these  varie- 
ties are  all  descended  from  a  common  stock,  their 
existence  is  proof  that  a  great  amount  of  change 
is  constantly  taking  place  in  the  structure  of  our 
species. 

A  word  as  to  the  amount  of  the  individual  varia- 
tions. The  changes  which  occur  in  single  individuals 
are  of  all  grades,  great  and  small.  Sometimes  they 
are  so  minute  that  only  a  practised  eye  can  see 
them,  while  on  the  other  hand  they  may  be  so  great 
as  to  be  almost  incredible.  The  pug  dog,  the  short- 
faced  tumbler  pigeons,  the  hook-billed  ducks  ap- 
peared suddenly  in  nearly  the  same  state  in  which 
we  now  find  them.  We  thus  see  that  the  modifica- 
tion of  species  through  variation  may  be  a  slow 
continual  process  of  accumulation  of  minute  varia- 
tions ;  or  it  may  be  an  interrupted  process  occurring 
by  a  series  of  greater  or  lesser  jumps.  It  is  true  that 
it  is  seldom  possible  in  the  case  of  wild  animals  to 
determine  by  direct  observation  that  these  individual 
variations  are  transmitted  from  generation  to  genera- 
tion. But  the  existence  of  varieties  in  nature  which 
do  breed  true  is  a  sufficient  proof  that  such  is  the 
case.  Moreover  in  some  instances  it  has  been  dK 
rectly  observed.  Perhaps  the  best  instance  of  the 
kind  is  a  series  of  experiments  of  a  Russian  natural- 
ist, Schmankewitsch.  These  experiments  were  upon 
a  species  of  Crustacea  (Artemia  Milhausenii)  which 


CAUSES  OF  VARIATION.  2/ 

lives  naturally  in  water  of  a  slight  degree  of  saltness. 
By  gradually  raising  the  percentage  of  salt  this  ex- 
perimenter succeeded  in  transforming  this  species 
into  an  entirely  different  one  (A.  Salind),  and  by 
reversing  the  process  he  transformed  the  latter 
species  into  the  former.  Nor  was  this  all.  Still 
further  freshening  the  water  by  gradual  changes,  he 
succeeded  in  transforming  this  same  species  into  still 
another,  which  was  so  very  different  from  the  first 
that  it  had  previously  been  ranked  as  a  distinct 
genus  (Branchippus).  These  changes  took  place 
slowly,  several  generations  being  required  for  the 
complete  transformation,  showing  that  the  indi- 
vidual variations  were  transmitted  from  one  genera- 
tion to  another,  increasing  in  importance  with  each 
generation.  All  of  these  species  had  been  known 
before,  and  had  always  been  considered  as  distinct 
species  and  genera.  Here  was  actual  proof  of  their 
genetic  connection  with  each  other.  It  is  important 
to  notice  that  this  naturalist  was  led  to  carry  on  his 
experiments  by  seeing  them  performed  by  nature  on 
a  grand  scale  by  the  gradual  freshening  of  a  salt- 
water lake.  This  instance  is,  therefore,  enough  to 
prove  that  not  only  do  variations  occur  under 
nature,  but  that  they  may  by  being  transmitted  be- 
come sufficiently  great  to  give  rise  to  varieties  which 
all  naturalists  rank  as  species. 

Causes  of  Variation. 

For  every  one  of  these  variations,  whether  it  be 
tfiinute  or  great  in  amount,  there  must  be  an  ade- 
quate cause.  But  in  regard  to  the  nature  of  these 


28  EVOLUTION  OF  TO-DAY. 

causes  there  is  much  difference  of  opinion.  The 
causes  of  the  variations  must  evidently  be  some- 
thing connected  with  the  organism  and  internal,  or 
something  outside  of  it.  We  can  suppose  that  all 
variation  is  due  to  the  action  of  external  condi- 
tions. Most  animals  have  two  parents  and  cannot, 
of  course,  be  like  both.  But  aside  from  this  fact, 
the  reason  that  a  child  differs  from  either  of  its 
parents  may  be  due  to  the  fact,  that  it  is  never 
under  the  same  conditions  as  its  parents.  All  varia- 
tion would  thus  be  dependent  on  the  action  of  the 
environment.  But  it  is  also  possible  to  suppose  that 
the  causes  of  variation  are  in  the  laws  of  the  organ- 
ism, and  only  indirectly  related  to  the  environment. 
If  this  were  true,  the  child  might  be  like  neither 
parent,  nor  even  midway  between  them,  though  the 
circumstances  were  all  alike. 

And  right  at  this  point  lies  the  difference  between 
most  of  the  modern  theories  of  evolution.  All  theo- 
ries are  based  fundamentally  upon  variations  which, 
we  have  seen,  are  so  abundant.  It  is  evident,  there- 
fore, that  the  particular  theory  which  any  one  may 
hold  as  to  evolution,  will  depend  upon  his  concep- 
tion of  the  causes  of  and  the  laws  governing  these 
variations.  Assuming,  for  a  moment,  that  new 
species  have  arisen  by  the  accumulation  of  such 
variations,  the  question  is  resolved  into  another  one, 
what  causes  the  variations  ?  The  answers  to  this 
question  have  been  numerous.  Darwin,  while  sup- 
posing that  all  of  the  variations  had  a  sufficient 
cause,  could  discover  no  sufficient  cause,  and 
thought  that  they  were  only  indirectly  related  to 


CAUSES  OF  VARIATION.  2Q 

external  conditions.  He  assumed,  therefore,  as  a 
basis  for  his  theory,  that  all  organisms  have  an  in- 
herent  tendency  to  vary.  In  accordance  with  this 
tendency,  every  individual  departs  more  or  less  from 
the  form  of  its  parents.  Such  departures  he  believed 
were  indefinite  and  irregular,  simply  being  the  re- 
sult of  a  tendency  to  change.  Darwin  came  to  this 
view  because  he  was  seldom  able  to  trace  any  definite 
connection  between  the  environments  of  an  organ- 
ism and  its  conditions.  Another  school,  which  is 
called  the  Neo-Lamarckian  school,  does  find  a 
definite  connection  between  the  organism  and  its 
environment.  The  representatives  of  this  school 
point  to  instances  increasing  every  day,  where  it  has 
been  shown  that  definite  changes  in  condition  in- 
duce definite  changes  in  animals.  They  show  that 
many  animals,  under  the  same  conditions,  vary  in 
the  same  or  in  parallel  directions.  They  point  to 
numerous  instances  where  changes  in  locality  pro- 
duce definite  changes  in  structure — such  as  the  case 
above  mentioned  of  American  birds.  They  con- 
clude, therefore,  that  we  are  to  look  at  the  environ- 
ment exclusively  for  the  cause  of  variation  ;  and 
they  say  that  if  we  find  any  series  of  variations  ac- 
cumulated generation  after  generation,  it  is  because 
the  same  external  conditions  continue  to  produce 
them.  Some  naturalists  believe  in  an  internal  law, 
which  is  supposed  to  have  charge  over  variations, 
and  to  regulate  them  independently  of  external  con- 
ditions. In  accordance  with  this  supposed  law,  any 
amount  of  variation  may  appear  suddenly,  without 
any  external  factor  for  bringing  it  into  existence. 


30  EVOLUTION  01'  TO-DA  Y. 

This  law  differs  from  Darwin's  "  inherent  tendency  "" 
to  vary,  in  that  it  is  supposed  to  produce  definite 
changes  rather  than  chance  variations. ,  And  there 
are  not  wanting  facts  which  give  support  to  this 
view.  In  the  case  of  domestic  races,  it  is  easy  to 
show  that  the  variations  are  not  indefinite,  being  to 
a  certain  extent  confined  to  special  directions  ;  and  it 
is  also  plain  that  this  definiteness  is  not  wholly  ex- 
plained by  external  conditions.  The  pigeons,  for 
instance,  vary  in  some  directions,  but  not  in  others. 
They  show  no  tendency  to  develop  the  bill  of  the 
humming  bird  or  the  plumage  of  the  bird  of  paradise  ; 
nor  is  there  the  slightest  reason  for  thinking  that 
they  would  do  so  if  placed  in  the  same  conditions. 
Moreover,  the  pigeon  varies  with  the  greatest  of 
readiness,  while  some  other  animals — such  as  the 
goose — scarcely  vary  at  all.  Many  instances  of 
this  kind  might  be  selected,  to  show  that  variations 
are  not  indefinite,  not  entirely  dependent  on  the  en- 
vironment, but  are  regulated,  to  some  extent,  either 
by  natural  laws  or  by  the  nature  of  the  organism. 
Still  other  views  of  the  nature  of  variations  are 
held.  Indeed,  the  facts  of  variation  are  so  extremely 
numerous;  they  have  been  collected  under  such 
very  different  circumstances,  and  by  so  many 
hundreds  of  people  ;  they  are  so  very  varied  in 
their  seeming  import ;  and,  above  all,  so  great  is 
our  ignorance  of  the  conditions  of  animals,  even 
when  we  seem  to  be  well  acquainted  with  them, 
that  it  would  hardly  be  possible  to  invent  any  law 
of  variation  which  could  not  be  attested  by  some 
facts. 


LIMITS  OF  VARIATION.  3! 

Two  conclusions  can  at  least  be  unhesitatingly 
drawn  :  i.  Variations  are  partly  dependent  upon 
external  conditions.  2.  They  are  not  wholly  so  de- 
pendent. 

Limits  of  Variation. 

A  very  great  amount  of  variation  is  thus  proved 
and  everywhere  admitted.  The  question  for  discus- 
sion is  not  as  to  its  existence  but  as  to  its  limitation. 
Is  it  unlimited  ?  Can  any  variation  go  on  increasing 
generation  after  generation,  until  new  species  arise 
by  a  continual  accumulation  of  variations?  Evi- 
dently if  these  variations  are  not  limited,  but  can 
continue  indefinitely,  becoming  greater  with  suc- 
ceeding generations,  the  final  result  would  be  such 
great  differences  between  animals  as  to  form  new 
species.  And  this  is  the  position  that  is  held  by 
most  evolutionists,  though  not  by  all.  New  species 
are  believed  to  have  arisen  by  the  accumulation  of 
variations,  each  slight  in  amount,  but  when  added 
together  becoming  sufficient  to  constitute  the  differ- 
ences between  species.  Variations  are  thus  consid- 
ered as  unlimited.  It  must,  of  course,  be  'true 
that  there  are  certain  limits  set  upon  variation  by 
physical  conditions.  Our  race-horses,  for  instance, 
have  been  continually  increasing  their  speed  since 
racing  has  become  common.  No  limit  to  this  varia- 
tion has  as  yet  been  reached.  But  evidently  there 
must  be  a  limit  to  this  increase  in  speed  toward 
which  horses  can  tend  but  beyond  which  they  can- 
not go.  So  in  other  features  ;  it  is  usually  possible 
to  see  a  limit  to  variation  set  by  physical  conditions. 


32  EVOLUTION  OF  TO-DAY. 

But  the  evolutionist  says  that  these  are  the  only 
limits.  He  tells  us,  moreover,  that  in  most  cases 
these  physical  limits  are  so  distant  that  there  is 
abundant  opportunity  for  many  new  species  to  arise 
before  they  are  reached. 

But  those  who  believe  in  special  creation,  and  at 
least  one  prominent  naturalist  who  accepts  evolu- 
tion, claim  that  there  are  other  limits.  These  limits 
are  internal  and  form  the  boundary  line  between 
species.  Animals  may,  it  is  said,  vary  in  any  direc- 
tion within  these  limits,  but  can  never  exceed  them. 
A  pigeon  may  vary  very  much,  but  it  never  ceases 
to  be  a  pigeon.  Simple  variation  can  never  produce 
a  new  species,  but  only  varieties  of  the  old  species. 
And  this  brings  us  to  the  real  subject  of  this  chap- 
ter— the  immutability  of  species. 

Are  Species  Stable? 

The  question  we  are  to  consider  is  this :  Can 
variations,  by  continual  accumulations,  become  so 
great  as  to  form  new  species  ;  or  are  there  boundary 
lines  between  species  beyond  which  variation  cannot 
extend  ? 

What  is  a  species  ?  Can  this  term  be  so  accurately 
defined  as  to  make  it  possible  to  decide  whether  the 
variations  occurring  are  always  within  the  limits  of 
the  species,  or  whether  they  may  not  exceed  them  ? 

The  answer  to  this  question  is,  unfortunately,  No. 
Naturalists  are  unable  to  tell  us  what  a  species  is 
and  what  a  variety.  The  greatest  confusion  exists 
in  the  various  systems  of  classification.  No  two 
systematists  agree  as  to  their  classification.  Forms 


ARE   SPECIES  STABLE?  33 

ranked  by  one  as  true  species  are  ranked  by  another 
as  simple  varieties.  If  two  animals  are  quite  like 
each  other  they  will  usually  be  called  varieties  ;  if 
quite  unlike  they  will  be  called  species.  But  no  one 
has  been  able  to  tell  us  how  a  line  can  be  drawn  by 
which  we  can  decide  whether  two  forms  are  unlike 
enough  to  be  called  species.  This  confusion  makes 
it  utterly  impossible  to  come  to  any  conclusion  as  to 
the  mutability  of  species.  Species  are  .  generally 
considered  to  be  so  distinct  as  not  to  be  connected 
by  intermediate  forms,  while  varieties  are  thus  con- 
nected. If,  therefore,  the  evolutionist  shows  that 
any  two  well-defined  species  are  thus  connected, 
they  immediately  lose  their  rank  as  species  and  be- 
come simple  varieties.  Thus  the  whole  force  of  the 
proof  is  lost.  When,  as  above  described,  the  Rus- 
sian naturalist  showed  that  Artemia  could  be  con- 
verted into  Branchippus,  it  would  seem  that 
something  had  been  proved.  These  forms  had 
always  been  considered  distinct  species,  and  doubt- 
less would  have  been  so  regarded  were  it  not  for 
this  demonstrated  connection  between  them.  But 
now  it  is  evident  that  they  can  be  regarded  as  the 
fresh-  and  salt-water  varieties  of  the  same  species. 
Indeed,  they  must  be  so  regarded  or  the  immuta- 
bility of  species  is  proved.  Thus  the  argument  is 
inevitably  in  a  circle.  The  naturalist,  by  long  study, 
succeeds  in  uniting,  by  intervening  varieties,  two 
forms  which  are  considered  as  distinct  species,  only 
to  have  the  satisfaction  of  seeing  that  he  has  shown 
them  to  be  varieties  of  one  species.  And  thus,  un- 
til a  very  large  number  of  species  have  been  united, 
this  phantom  chase  will  continue. 


34  EVOLUTION  OF  TO-DAY. 

The  only  really  logical  distinction  ever  given  to 
separate  species  and  varieties  is  that  of  the  sterility 
of  species  when  crossed,  and  the  fertility  of  varie- 
ties under  the  same  conditions.  It  is  said  that 
species  cannot  interbreed  with  each  other,  while  all 
varieties  are  perfectly  fertile  when  crossed.  This 
gives  a  new  understanding  of  species  and  varieties. 
The  difference  between  the  two  is  not  in  any  amount 
of  difference  in  bodily  structure,  but  in  affiliation. 
All  the  varieties  of  a  species  are  believed  to  have 
descended  from  the  same  parent,  and  can  conse- 
quently breed  with  each  other.  Different  species, 
however,  have  not  thus  been  connected,  and  can- 
not interbreed.  Sterility  is  thus  regarded  as  a  bar 
set  by  the  Creator  to  prevent  the  confusion  which 
would  result  from  crossing.  It  is  upon  this  distinc- 
tion that  those  who  believe  in  the  stability  of  species 
found  most  of  their  argument.  If  this  be  ad- 
mitted as  the  definition  of  a  species,  the  question 
can  at  least  be  discussed,  although  open  still  to  the 
phantom  chase  above  mentioned.  Here  is  a  limit 
beyond  which  it  is  claimed  variations  cannot  go. 
It  is  pointed  out  that  so  far  as  our  observations  have 
gone,  no  amount  of  variation  has  ever  produced  a 
new  species,  if  this  be  admitted  as  a  distinction.  In 
no  case  has  variation  produced  among  domestic  varie- 
ties any  degree  of  sterility.  All  of  our  breeds  of 
pigeons,  as  widely  different  as  they  are,  can  breed 
freely  with  each  other ;  all  of  the  numerous  and 
diverse  breeds  of  dogs  are  perfectly  fertile  inter  se  ; 
and  so  with  domestic  races  in  general.  Indeed  Dar- 
win himself  admits  that  he  knows  of  no  well- 


ARE   SPECIES  STABLE?  35 

authenticated  case  of  domestic  races  being  sterile 
when  crossed,  a  fact  which  he  considers  extraordi- 
nary, considering  the  great  difference  between  do- 
mestic breeds  of  dogs,  fowls,  pigs,  etc.,  and  the  very 
slight  differences  between  natural  species  which  are 
sterile  inter  se.  So  far,  then,  as  experiments  on  do- 
mestic animals  are  concerned,  the  evidence  seems 
to  indicate  that  no  amount  of  ordinary  accumula- 
tion of  variations  is  able  to  produce  forms  so  differ- 
ent as  to  be  infertile  when  crossed.  If,  then,  this  be 
accepted  as  a  criterion  for  specific  distinction,  there 
is  no  case  on  record  where  there  has  been  even  an 
approximation  toward  the  production  of  a  new 
species. 

Possibly  the  human  race  may  be  a  partial  case  in 
hand.  The  races  of  men  are  to-day  pretty  univer- 
sally admitted  to  be  simple  varieties  of  a  single 
species.  The  different  races  are  well  known  to  be 
fertile  when  crossed,  a  fact  attested  by  half-breeds 
of  all  sorts.  But  it  frequently  appears  that  half- 
breeds  form  a  somewhat  weak  race,  having  lost  the 
vigor  of  either  parent.  Particularly  is  this  true 
when  half-breeds  intermarry.  It  is  stated  by  Broca 
that  in  some  cases  the  fertility  is  not  kept  up  for 
many  generations,  unless  the  pure  blood  of  one  of 
the  parents  is  introduced.  This  is  true  he  says  of 
the  cross  between  the  Australian  and  European 
races.  It  is  frequently  stated  that  mulattoes  are 
not  very  fertile,  and  soon  become  sterile  unless  the 
pure  blood  of  one  of  the  races  is  once  more  intro- 
duced. But  all  of  these  statements  are  denied. 
Others  who  have  studied  the  matter  claim  that  all 


36  EVOLUTION  OF  TO-DAY. 

half-breeds  are  fertile  for  an  indefinite  period,  and 
sometimes  even  more  so  than  the  pure  breeds. 
This  subject  has  in  the  past  become  so  much  in- 
volved in  theological  discussions  as  to  make  it  some- 
what difficult  to  know  what  is  the  true  state  of  the 
case.  It  is  not  possible,  therefore,  to  say  definitely 
whether  or  not  man  can  be  cited  as  a  case  where 
varieties  have  a  certain  amount  of  sterility.  The 
evidence  for  such  a  conclusion  is  at  all  events  very 
slight. 

Finding,  then,  no  cases  where  domestic  varieties 
are  sterile  when  crossed,  naturalists  have  attempted 
to  meet  the  difficulty  in  another  way.  They  have 
questioned  this  definition  of  species  by  showing  that 
true  species  are  not  always  sterile  when  crossed. 
In  accordance  with  the  idea  that  sterility  is  a  bar 
which  has  been  laid  down  to  separate  species,  it  is 
difficult  to  see  how  there  could  be  any  grades  of 
sterility.  We  should  expect  either  that  all  species 
would  be  sterile  when  crossed,  or  they  would  all  be 
equally  fertile.  But  investigations  have  certainly 
shown  that  sterility  is  no  such  rigid  bar  as  this.  It 
is  true  that  species  are  usually  sterile  when  crossed, 
but  the  amount  of  fertility  is  a  variable  quantity. 
Many  species  do  not  produce  any  young  when 
crossed;  while  many  others  do  produce  young, 
which  are  themselves  incapable  of  reproduction. 
And  in  still  other  cases  even  this  amount  of  sterility 
is  not  found. 

Owing  to  the  difficulty  of  experimenting  upon 
animals,  observations  upon  this  question  have  been 
more  largely  confined  to  plants  than  is  desirable. 


ARE   SPECIES  STABLE?  37 

Among  plants,  at  all  events,  there  are  many  in- 
stances of  hybrids  between  species  being  perfectly 
fertile,  and  continuing  so  for  an  indefinite  period. 
Experiments  during  the  last  twenty-five  years  have 
increased  the  number  of  such  fertile  crosses  many 
fold.  Direct  experiments  upon  plants  are  very 
easily  carried  on,  for  the  pollen  can  readily  be  trans- 
fered  from  one  plant  to  another.  By  these  experi- 
ments, so  great  an  amount  of  crossing  has  been 
found  possible,  that  one  writer  comes  to  the  conclu- 
sion that  fertility  of  hybrid  plants  is  the  rule  and 
sterility  the  exception.  So  far  as  plants  are  con- 
cerned, there  is  not  the  slightest  ground  for  consid- 
ering sterility  as  a  distinctive  bar,  separating  species. 
Animals  are  not  so  easy  to  study,  and  the  diffi- 
culties in  the  way  of  experimenting  have  prevented 
any  extended  observations.  Of  course,  only  those 
animals  under  confinement  can  be  studied,  and  con- 
finement always  produces  great  changes  in  the  repro- 
ductive function.  Some  animals  will  not  breed  at  all 
when  in  a  state  of  captivity  or  domestication,  while 
others  appear  to  breed  more  freely  than  in  their  na- 
tural condition.  It  is  difficult  to  get  two  species  to 
unite  so  as  to  make  it  possible  to  discover  whether  or 
not  they  are  fertile.  But  nevertheless  quite  a  num- 
ber of  cases  of  cross-breeding  are  known.  Two 
species  of  apes,  belonging  to  different  genera,  have 
crossed  and  produced  young  ;  the  rabbit  and  the 
hare  very  commonly  cross  ;  the  tiger  has  bred  with 
the  lion  ;  the  leopard  with  the  jaguar ;  the  polar 
bear  with  the  brown  bear ;  various  species  of  the 
horse  family  have  repeatedly  crossed.  A  hybrid 


38  EVOLUTION  OF  TO-DAY. 

snake,  between  two  genera,  was  born  in  the  Zoologi- 
cal Gardens  of  London.  Hybrid  ducks  are  common 
and  hybrid  fishes  are  easily  produced.  In  most  of 
these  cases  the  hybrids  thus  produced  are  them- 
selves sterile.  But  this  is  not  true  of  all.  The 
cross  between  the  rabbit  and  the  hare,  two  good 
species,  is  perfectly  fertile.  The  cross  between  the 
dog  and  the  jackal,  or  the  dog  and  the  wolf  or  fox, 
remains  fertile,  for  a  number  of  generations  at  least. 
The  common  goose  and  the  Chinese  goose  when 
crossed  produce  perfectly  fertile  offspring  ;  and  hy- 
brids between  the  mallard  and  muscovy  ducks  show 
no  sterility.  Infertility  of  hybrids  is  by  no  means  a 
universal  law,  among  domestic  species  at  all  events. 
But  a  similar  hybridity  has  been  observed  among 
animals  in  a  state  of  nature.  A  cat  has  been  de- 
scribed by  Cuvier,  which  is  a  cross  between  the  do- 
mestic cat  and  Felis  Bangalensis.  A  hybrid  duck  is 
known  to  exist  in  nature,  and  no  less  than  eight 
hybrid  fresh-water  fishes  are  known  in  Germany. 
The  polecat  and  the  ferret  produce  hybrids.  A  male 
white  cockatoo  and  a  female  rose-colored  cockatoo, 
which  never  bred  in  confinement,  were  set  at  liberty 
in  the  woods,  and  bred  together  for  two  years.  It 
is,  of  course,  impossible  to  say  whether  hybrids  are 
themselves  fertile  or  not,  for  no  observations  are 
possible. 

A  careful  examination  of  the  facts  of  cross-breed- 
ing, collected  by  our  ablest  experimenters,  reveals 
thus  several  significant  facts.  It  is  true  that  in  a 
great  majority  of  cases  a  certain  amount  of  sterility 
results  from  the  crossing  of  distinct  species.  But 


ARE   SPECIES  STABLE?  39 

this  sterility  is  a  variable  quantity.  Some  species 
will  not  unite  at  all,  or  if  they  do  will  produce  no 
young.  Others  will  produce  young  occasionally,  but 
these  young  are  sterile.  Some  produce  young, 
which  in  their  turn  occasionally  reproduce.  And  so 
on ;  cases  can  be  selected  with  constantly  increasing 
fertility,  until  in  some  extreme  instances  the  fertility 
of  hybrids  seems  slightly  greater  than  that  of  the 
legitimate  young.  The  power  of  hybrids  to  repro- 
duce varies  from  zero  to  absolute  fertility.  Again, 
it  is  the  rule  that  varieties  are  fertile  when  crossed, 
but,  according  to  the  best  experimenters,  there 
are  also  exceptions  to  this  rule. 

The  ability  of  two  species  to  interbreed  does  not 
depend  upon  the  amount  of  structural  difference 
between  them,  for  it  is  found  that  some  species 
which  are  very  closely  related  will  not  cross,  while 
others  much  more  unlike  will  cross  with  the  greatest 
facility.  It  is  frequently  found  that  reciprocal 
crosses  produce  very  different  results  ;  for  the  male 
of  one  species  may  cross  with  the  female  of  another 
and  readily  produce  young,  while  the  female  of  the 
first  species  can  cross  with  the  male  of  the  second 
only  with  difficulty.  The  cross  between  the  ass  and 
the  horse  is  a  case  in  point.  The  mule  is  obtained 
readily  as  the  cross  between  the  male  ass  and  the 
female  horse  ;  but  the  attempt  to  get  a  cross  in  the 
other  direction  is  rarely  successful.  It  sometimes 
happens  that  all  of  the  species  of  a  genus  will  cross 
with  the  others  except  one,  and  this  one,  in  structure 
no  more  different  than  the  rest,  will  not  hybridize 
with  any  of  the  others.  Differences  of  this  kind 


4O  EVOLUTION  OF  TO-DAY. 

are  also  found  in  individuals,  the  ease  with  which 
crosses  can  be  made  varying  very  much  in  different  in- 
dividuals of  the  same  species.  Occasionally  species 
which  are  very  difficult  to  cross  produce,  when  they 
do  cross,  offspring  which  are  very  fertile  ;  and  species 
which  cross  with  great  ease  produce  absolutely 
sterile  hybrids.  And  it  is  important  to  notice  that 
the  best  experimenters  not  unfrequently  disagree  in 
regard  to  the  very  same  species;  some  claiming 
that  given  species  are  fertile  when  crossed,  and  others 
claiming  that  they  are  sterile. 

Now  all  of  these  facts  do  show  one  thing,  viz. : 
that  sterility  of  species,  when  crossed,  is  no  definite 
law.  Sterility  is  a  variable  matter.  It  is  not  de- 
pendent upon  specific  limits,  nor  upon  the  closeness 
of  the  relations  of  the  species  crossed,  but  upon 
some  other  factors  not  easily  discovered.  It  is  plain 
from  all  these  cases  that  sterility  is  not  a  bar  which 
rigidly  separates  species  from  each  other.  Natural- 
ists have  proved  that  this  distinction  between  species 
and  varieties  is  not  absolutely  correct.  Whatever 
be  our  belief  as  to  the  origin  of  species,  we  cannot 
believe  that  each  was  created  with  the  bar  of  sterility 
to  separate  it  from  others. 

Why,  then,  are  species  usually  sterile  when 
crossed  ?  If  this  is  not  a  created  bar,  how  did  it 
arise  ?  We  have  seen  that  ordinary  variations  have 
not  yet  been  shown  to  give  rise  to  sterility.  From 
various  considerations  most  scientists  are  to-day  in- 
clined to  accept  the  view  that  it  is  due  largely  if  not 
entirely  to  differences  in  the  sexual  organs  indepen- 
dently of  differences  in  the  rest  of  the  body.  Two 


ARE   SPECIES  STABLE?  4! 

species,  very  much  alike  in  other  respects,  may  have 
their  sexual  organs  very  dissimilar,  and  sterility 
would  be  the  result,  while  two  other  species,  or  va, 
rieties,  while  very  unlike  in  most  features,  might 
have  their  sexual  organs  so  similar  as  to  produce 
perfect  fertility.  If  this  is  true,  we  reach  a  new  dis- 
tinction of  species  and  varieties.  The  differences 
between  varieties  may  affect  any  part  of  the  body 
except  the  sexual  organs.  Differences  between 
species  include,  as  a  rule,  also  the  sexual  organs. 

It  is  now  possible  to  see  some  reason  why  our 
domestic  races  continue  fertile.  These  races  have 
been  produced  by  selection  on  the  part  of  the 
breeders,  who  do  not  pay  any  attention  to  the  sex- 
ual organs  in  their  selection.  The  general  differ- 
ences may  therefore  become  very  great  without 
producing  sterility.  Moreover,  there  is  very  good 
reason  for  believing  that  domestication  has  the 
effect  of  making  many  animals  more  readily  suscep- 
tible to  cross-breeding.  Our  various  breeds  of  dogs, 
for  instance,  are  almost  certainly  descended  from 
several  wild  stocks  which  must  once  have  been  dis- 
tinct species.  But  to-day,  all  dogs,  with  the  excep- 
tion of  certain  South  American  indigenous  species, 
breed  freely  with  each  other.  Now  either  these 
wild  stocks  originally  could  interbreed,  or,  what  is 
more  probable,  they  have  acquired  the  power  by 
domestication.  If  it  is  thus  true  that  domestication 
sometimes  produces  greater  fertility  in  this  way, 
another  suggestion  is  found  in  the  fact  for  the  fer- 
tility of  domestic  races. 

In  spite  of  all  these   facts  and  suggestions,  this 


42  EVOLUTION  OF  TO-DAY. 

matter  of  cross-breeding  raises  a  very  serious  diffi- 
culty for  those  evolutionists  who  believe  that  species 
arise  by  the  accumulation  of  variations.  The  diffi- 
culty lies  not,  however,  in  the  fact  that  species  are 
usually  sterile  when  crossed.  This  is  easily  under- 
stood, as  soon  as  sterility  is  found  to  be  variable,  by 
supposing  that  species  have  become  so  much  unlike 
that  cross-breeding  is  no  longer  possible.  The  diffi- 
culty lies  in  the  fact  that  no  amount  of  variation  in 
our  domestic  races  has  produced  any  sterility.  It  is 
not  possible  here  to  plead  a  lack  of  time,  since  a 
glance  at  domestic  races  shows  that  there  has  been 
time  enough  to  produce  enormous  changes,  much 
greater  than  those  which  separate  wild  species. 
Science,  indeed,  knows  very  little  of  the  causes  of 
sterility.  Elephants,  when  kept  in  a  state  of  only 
partial  captivity  in  their  native  country,  are  unable 
to  breed.  And  yet  two  of  them  in  the  hands  of 
American  showmen  did  produce  young,  under  con- 
ditions differing  as  widely  as  possible  from  those  of 
their  native  country.  When  science  can  explain 
this,  it  will  probably  be  able  to  tell  why  some  varie- 
ties are  sterile  when  crossed,  while  most  are  fertile, 
and  why  some  species  can  breed  freely  together, 
though  the  rule  is  almost  absolute  sterility.  At 
present,  however,  this  explanation  is  lacking,  and  it 
is  useless  to  deny  that  Darwinianists  are  embarrassed 
by  the  continued  fertility  of  our  domestic  races. 

Most  of  the  evidence  which  concerns  the  origin  of 
species  from  varieties  must  be  obtained  from  do- 
mestic animals,  since  these  alone  can  be  carefully 
observed.  Our  domestic  varieties  are  regarded  by 


ARE   SPECIES  STABLE?  43 

most  evolutionists  as  incipient  species.  It  has  been 
frequently  urged  as  an  argument  against  this  view, 
that  when  allowed  to  run  wild  these  varieties  return 
to  their  original  condition,  all  of  these  acquired 
peculiarities  disappearing.  This  is  thought  to  show 
that  domestic  varieties,  and,  therefore,  presumably 
all  varieties,  are  simply  oscillations  from  a  central 
form,  to  which  return  is  made  as  soon  as  opportunity 
admits.  This  is,  of  course,  an  argument  for  specific 
stability.  But,  really,  there  is  no  ground  for  the 
argument.  It  is  simply  an  assumption  that  these 
varieties  return  to  their  former  ancestral  condition. 
In  most  cases,  naturalists  do  not  know  what  the 
aboriginal  stock  was,  and  it  is,  therefore,  impossible 
rightly  to  make  any  such  assumption  as  that  on 
which  this  claim  is  founded.  It  is  true  that  our 
domestic  races  do  change  very  much  when  they 
become  wild.  But  this  is  not  surprising.  That  our 
carefully  selected  varieties  should  disappear  under  a 
return  to  the  feral  condition,  is  a  matter  of  course. 
They  have  been  produced  under  peculiar  circum- 
stances, and  by  very  careful  breeding.  It  would,  of 
course,  follow,  that  as  soon  as  these  circumstances 
are  withdrawn  the  peculiar  varieties  would  disap- 
pear. So  long  as  the  conditions  remain  constant, 
the  varieties  do  not  have  any  tendency  to  revert  to 
any  former  type,  and  this  is  all  that  the  theory  of 
evolution  requires. 

It  is  true  enough  that  naturalists  have  been 
unable  to  find  a  single  unquestionable  instance  of 
the  production  of  a  new  species.  It  has  been, 
therefore,  assumed  by  some  who  admit  the  theory 


44  EVOLUTION  OF  TO-DAY. 

of  evolution  in  general,  that  nature  is  not  forming 
any  new  species  to-day,  but  only  varieties.  This  is, 
however,  nothing  but  an  assumption.  Among  do- 
mestic varieties  it  is  true  that  the  methods  of  selec- 
tion have  not  succeeded  in  inducing  sterility  among 
the  varieties.  In  some  instances,  on  the  contrary, 
they  have  probably  rendered  mutually  fertile,  forms 
originally  sterile.  But  the  variations  have  been 
very  great,  and  have  been  sufficient  to  constitute 
distinct  species  and  genera  in  every  respect  except 
this  one  of  sterility.  In  the  great  realm  of  nature 
it  is  impossible  to  say  whether  or  not  new  species 
are  being  constantly  produced.  New  species  are 
certainly  being  constantly  found.  Since  the  fauna 
and  flora  are  not  thoroughly  known  in  any  country, 
new  species  may  be  constantly  appearing  without 
the  possibility  of  their  being  discovered.  Even  in 
England,  the  country  whose  fauna  is  best  known, 
new  species  are  occasionally  being  found.  It  is  only 
twenty-five  years  since  the  matter  has  been  consid- 
ered so  important,  and  this  is  too  short  a  time  to 
make  negative  conclusions  of  any  value.  Naturalists 
are  now  collecting  and  carefully  studying  the  spe- 
cies of  various  localities,  and  are  slowly  gathering 
data  for  an  answer  to  this  question.  When,  in  another 
century,  naturalists  can  compare  the  world  which 
they  know,  with  the  record  left  by  naturalists  to- 
day, it  may  be  possible  to  answer  this  question. 
But  to-day  the  problem  cannot  hope  for  immediate 
solution.  To  state  that  no  new  species  are  now 
forming,  is  not  only  to  beg  the  whole  question  at 
issue,  but  is  to  make  a  statement  for  which  the 


INDIRECT  EVIDENCE.  45 

only  evidence  is  the  fact  that  domestic  races  are 
fertile  when  crossed.  Considering  all  that  is  known 
as  to  the  fertility  of  hybrids,  this  is  certainly  too 
slim  a  basis  to  authorize  the  assumption  of  the 
whole  question. 

Indirect  Evidence. 

Not  having  time  enough  at  their  disposal  and  not 
being  able  to  define  the  term  species,  naturalists  are 
still  unable  to  decide  by  direct  evidence  whether  or 
not  species  are  immutable.  If  the  evidence  that 
species  have  been  derived  from  each  other  ceased 
here,  few  would  be  inclined  to  accept  evolution. 
But  there  is  a  large  amount  of  indirect  evidence 
bearing  upon  the  question.  If  species  have  arisen 
by  the  process  above  described,  certain  relations 
would  necessarily  follow.  It  is  the  exact  accord  of 
all  the  evidence  collected  with  these  necessary  rela- 
tions, which  has  caused  such  a  wide  acceptance  of 
organic  evolution.  Such  evidence  is  indirect,  but  it 
is  none  the  less  forcible.  In  the  following  four 
chapters  this  evidence  will  be  chiefly  discussed,  but 
a  word  of  preliminary  introduction  is  here  desirable. 

When  we  come  to  examine  the  relations  of  true 
species,  we  find  many  points  which  suggest  genetic 
relation.  As  already  mentioned,  no  naturalists  have 
been  able  to  distinguish  in  nature  between  species 
and  varieties.  All  grades  can  be  found  between 
two  similar  varieties  and  two  very  distinct  species. 
Indeed  among  the  sponges  careful  students  have 
been  unable  to  find  any  thing  which  they  can  call 
species  ;  for  the  whole  group  is  connected  together 


46  EVOLUTION  OF  TO-DAY. 

by  minute  gradations.  These  connecting  links  are 
not  so  prominent  elsewhere,  but  they  can  be  found 
in  all  groups  of  animals.  It  is  not  to  be  understood 
from  this,  however,  that  there  is  no  difference  be- 
tween species  and  varieties  ;  the  former  show  much 
greater  differences  than  the  latter,  and  are  usually 
more  stable.  But  there  is  no  marked  line  between 
them.  If  we  examine  the  relations  of  species  to  each 
other  and  compare  them  with  the  relations  of  varie- 
ties, a  strict  parallel  can  be  drawn.  The  large  num- 
ber of  domestic  pigeons,  with  their  numerous  races, 
can  be  divided  into  groups  and  sub-groups  corre- 
sponding exactly  to  the  divisions  which  are  found 
in  nature  of  genera  and  species.  It  is  only  neces- 
sary to  imagine  the  mutual  fertility  to  disappear, 
and  these  groups  would  resemble  in  every  respect 
the  natural  grouping  of  genera  and  species.  In 
other  words,  the  working  of  nature  in  accumulating 
variations  produces  results  which,  if  carried  far 
enough,  would  give  relations  exactly  such  as  are 
found  existing  between  species. 

Turning  to  fossil  deposits  there  is  in  some  cases 
evidence  amounting  to  practical  proof  that  species 
can  arise  in  this  way.  The  best  illustration  of  this 
is  found  in  the  Steinheim  Lake  deposit.  At  Stein- 
heim,  in  Wurtemberg,  there  is  a  large  deposit  of 
shells  which  has  been  subject  to  special  study.  The 
deposit  represents  the  bed  of  an  old  lake,  and  it 
appears  that  in  Tertiary  times  there  migrated  into 
this  lake  a  species  of  fresh  water  mollusk,  called 
Planorbis.  This  animal  found  an  unoccupied  field 
in  this  lake,  and  multiplied  rapidly.  As  fast  as  the 


INDIRECT  EVIDENCE.  47 

animals  died,  their  shells  sank  to  the  bottom  of  the 
lake  and  there  accumulated  for  ages.  The  shells 
are  now  found  in  this  old  lake-bottom  in  great 
quantities,  and  being  found  as  they  are  in  layers, 
the  whole  history  of  the  animals  can  be  studied  by 
examining  successive  layers.  And  most  beautifully 
has  such  study  shown  the  origin  of  species.  Begin- 
ning with  a  few  sample  varieties,  there  is  a  rapid 
divergence  until  very  diverse  forms  are  reached,  so 
diverse,  indeed,  that  they  must  unhesitatingly  be  set 
down  as  different  species.  At  least  this  would  be 
the  fact,  were  it  not  that  all  these  diverse  forms  are 
connected  by  an  infinite  number  of  intermediate 
forms.  It  is  of  course  possible  to  claim  here,  as 
elsewhere,  that  we  are  simply  dealing  with  a  single 
highly  variable  species.  But  the  extreme  forms  are 
so  very  different  from  each  other  that  this  claim  is  a 
very  weak  one.  If  species  be  defined  as  forms  not 
connected  with  each  other  by  intermediate  grada- 
tions, of  course  nothing  is  to  be  said.  But  if  we 
use  any  other  definition  for  species  that  it  is  possi- 
ble to  apply,  the  Steinheim  Lake  appears  as  the 
site  of  the  origin  of  a  number  of  species  from  a 
common  ancestor. 

One  very  interesting  argument  for  the  common 
origin  of  the  species  of  any  genus,  is  found  in  a  class 
of  variations  called  reversions.  Animals  and  plants 
frequently  show  quite  suddenly  features  which,  upon 
close  examination,  are  found  to  be  the  characteris- 
tics of  their  ancestors — characteristics  long  since 
lost  but  suddenly  reappearing.  The  circumstances 
which  bring  about  these  reversions  are  quite  varied. 


48  EVOLUTION  OF  TO-DAY. 

The  most  common  is  the  crossing  of  two  quite  dif- 
ferent individuals.  If,  for  instance,  two  very  differ- 
ent breeds  of  pigeons  be  crossed,  there  is  a  great 
tendency  to  produce  young  quite  unlike  either  par- 
ent, but  resembling  the  rock  pigeon,  which  is  known 
to  be  the  ancestor  of  our  races  of  domestic  pigeons. 
This  tendency  to  reversion  can  always  be  found 
more  or  less  marked  in  domestic  races.  It  is  cer- 
tainly a  marvellous  thing  that  characteristics  which 
have  been  lost  for  many  generations  should  have 
thus  the  power  to  reappear.  Science  has  no  ex- 
planation to  offer  for  the  fact.  Such  reversions  are 
never  supposed  to  give  rise  to  new  varieties.  They 
are,  on  the  other  hand,  claimed  to  prevent  the 
formation  of  new  varieties.  It  is  said  by  those 
who  do  not  accept  the  unstability  of  species,  that 
these  reversions  keep  the  species  true,  by  con- 
tinually bringing  the  individuals  back  to  the  cen- 
tral type  when  they  depart  too  widely  from  it. 
Reversion  has,  however,  never  been  known  to  pro- 
duce such  a  result.  It  does  not  take  place  in  ordi- 
nary circumstances,  but  only  when  the  great  changes 
occur. 

But  these  reversions  are  frequently  of  great  assist- 
ance to  the  naturalist  in  enabling  him  to  trace  the 
history  of  varieties.  When  it  is  found  that  all  of 
our  domestic  pigeons  revert  in  this  manner  to  the 
rock  pigeon,  it  is  almost  sure  proof  that  this  rock 
pigeon  was  their  common  ancestor,  even  if  this  fact 
stood  alone.  Now  the  important  point  to  be  noticed 
is,  that  reversions  of  a  precisely  similar  character  occur 
among  the  species  of  a  genus.  For  instance,  when 


INDIRECT  EVIDENCE.  49 

the  horse  and  the  ass  are  crossed,  the  offspring  pos- 
sesses features  which  are  found  in  neither  parent. 
The  mule,  in  ninety  cases  out  of  a  hundred,  shows  a 
number  of  bars  on  the  legs,  and  several  stripes  on  the 
shoulders.  In  rare  instances  it  is  found  that  the 
horse  and  ass  of  pure  breed  possess  the  same  feat- 
ures, scattered  cases  having  been  observed  in  almost 
every  variety  of  horse  and  ass.  But  hybrids  almost 
always  show  them.  Not  only  the  hybrid  between 
the  horse  and  the  ass,  but  all  hybrids  of  the  various 
members  of  the  horse  family,  show  the  same  features. 
The  similarity  of  this  case  with  that  of  the  pigeons 
is  exact,  and  plainly  indicates  that  here  is  a  true  case 
of  reversion.  Now  in  the  pigeons  it  is  known  that 
the  reversions  refer  to  a  common  ancestor  of  the 
breeds  crossed.  It  is  certainly  a  legitimate  inference 
that  the  reversions  occurring  in  the  horse  family  also 
refer  to  a  common  ancestor.  When,  therefore,  we 
find  various  species  of  the  horse  family,  the  horse, 
the  ass,  the  zebra,  the  quagga,  the  hemionus,  all 
showing  this  tendency  to  reversion,  we  can  hardly 
avoid  the  conclusion  that  they  have  had  a  common 
ancestor.  Our  naturalists  have  even  thought  it  pos- 
sible to  tell  pretty  accurately  the  specific  features  of 
this  ancestor  of  the  horse  family,  drawing  their  con- 
clusions from  these  reversions,  together  with  other 
evidence.  The  common  ancestor  of  the  horse  family, 
they  tell  us,  was  an  animal  somewhat  smaller  than  the 
ass,  of  a  dun  color,  and  with  stripes  much  like  those  of 
the  zebra.  If  this  evidence  is  accepted,  it  is  plain 
that  the  common  origin  of  some  species  is  no  longer 
a  matter  of  question.  It  is  of  course  possible  to 


50  EVOLUTION  OF  TO-DAY. 

deny  that  these  features  are  really  reversions  to  a 
common  ancestor. 

Summary. 

If  animals  and  plants  produced  young  precisely 
like  themselves  there  would  be  no  possibility  for  a 
belief  in  evolution,  for  of  course  no  new  species  could 
arise  by  genetic  descent.  But  a  study  of  animals 
under  domestication,  where  they  can  be  carefully 
watched,  as  well  as  under  nature,  has  proved  that 
animals  do  not  produce  young  precisely  like  them- 
selves. Two  laws  are  found  to  govern  animals  in 
their  reproduction.  The  first  is  heredity;  and  in 
accordance  with  this,  species  tend  to  repeat  them 
selves  in  their  young.  The  second  is  variation  ;  and 
in  accordance  with  this  law  animals  produce  young 
which  are  in  many  features  unlike  their  parents. 
These  variations  in  the  young  are  very  numerous. 
They  are  sometimes  very  small  and  sometimes  very 
great.  They  are  transmitted  from  generation  to 
generation,  and  have  a  tendency  to  become  greater 
and  greater.  Each  variation  has  of  course  its  ade- 
quate cause,  either  in  the  organism  or  in  its  external 
conditions.  Occasionally  it  is  possible  to  discover 
their  causes,  but  in  most  cases  it  is  impossible. 
Plainly,  if  the  same  conditions  continue  to  act  upon 
organisms  for  many  generations,  the  variations  they 
produce  will  continue  to  increase.  And  this  is  found 
to  be  true.  By  the  accumulation  of  these  variations 
there  are  finally  formed  groups  within  the  species. 
Each  group  differs  in  certain  respects  from  the 
others,  though  they  all  show  so  much  likeness  that 
they  are  still  grouped  together  as  a  single  species. 


SUMMAR  Y.  51 

The  sub-groups  are  called  varieties,  and  are  every- 
where regarded  as  genetically  related  to  each  other. 
The  question  then  arises  as  to  whether  there  is  a 
limit  to  this  accumulation  of  variations.  It  is 
claimed  by  evolutionists  that  there  is  no  limit  ex- 
cept that  set  by  physical  conditions.  They  continue 
to  increase,  causing  the  varieties  to  become  more 
and  more  unlike,  until  they  finally  become  so  different 
that  cross-breeding  becomes  no  longer  possible  in  all 
cases.  Thus  individual  variations  become  varieties; 
and  varieties  become  species.  But  it  has  not  yet 
been  found  possible  to  prove  this  claim  by  direct 
evidence.  For  it  is  asserted  on  the  other  hand  that 
these  variations  are  not  accumulated  indefinitely, 
but  are  confined  within  certain  bounds.  The  limits 
thus  assumed  are  supposed  to  constitute  boundary 
lines  between  species.  In  attempting  to  define  these 
specific  limits,  it  has  been  found  impossible  to  dis- 
cern them  in  any  amount  of  structural  difference. 
The  differences  between  true  varieties  may  surpass 
those  between  species.  Such  a  limit  has  been  drawn 
at  the  point  of  sterility,  the  position  being  taken 
that  no  amount  of  ordinary  variation  can  cause  the 
varieties  thus  arising  to  become  mutually  sterile. 
The  evolutionists  have  been  unable  to  disprove  this 
claim  by  direct  evidence,  for  they  can  cite  no  in- 
stances where  varieties  have  become  unfertile.  But 
they  deny  the  correctness  of  this  definition,  showing 
that  sterility  is  not  a  rigid  bar  separating  species,  since 
in  some  cases  true  species  are  fertile  when  crossed  ; 
they  have  further  given  reason  for  believing  that 
sterility  is  caused  by  differences  in  the  sexual  organs. 


52  EVOLUTION  OF  TO-DAY. 

When  challenged  to  produce  a  new  species  by  varia- 
tion they  acknowledge  their  inability  to  do  so,  and 
demand  more  time.  Direct  evidence  is  therefore 
not  sufficient  either  to  prove  or  disprove  the  muta- 
bility of  species.  Meantime  the  scientist  claims  that 
he  can  bring  forward  enough  indirect  evidence  to 
substantiate  the  theory  of  evolution  ;  since  all  of  the 
facts  of  the  organic  world  appear  to  him  to  be  in 
conformity  with  the  belief  that  species  have  been 
evolved.  To  this  indirect  evidence  we  will  devote 
the  next  four  chapters. 


CHAPTER  II. 

THE   CLASSIFICATION    OF   THE    ORGANIC   WORLD. 
The  Existence  and  Significance  of  a  Classification. 

A  CERTAIN  writer  who  disbelieved  in  the  theory 
of  evolution  once  asked  Prof.  Huxley  where  he 
could  find  the  strongest  arguments  in  its  favor, 
which  he  acknowledged  he  desired  for  the  sake  of 
publicly  refuting  them.  Prof.  Huxley  advised  him 
to  take  a  course  of  study  in  comparative  anatomy. 
The  man  was  naturally  somewhat  angry  at  this 
unexpected  piece  of  advice  and  of  course  did  not 
follow  it.  But  Prof.  Huxley  knew  whereof  he  was 
speaking,  and  his  advice  was  full  of  wisdom  which 
no  one  can  appreciate  who  has  not  gained  experi- 
ence by  following  it,  and  making  a  careful  study  of 
the  animal  kingdom.  The  strongest  arguments 
which  are  found  in  favor  of  the  theory  of  descent, 
and  frequently  too,  many  of  the  most  significant 
difficulties,  come  from  the  innumerable  little  points 
which  familiarity  with  animals  brings  under  one's 
observation  ;  too  many  to  introduce  into  any  discus- 
sion for  the  sake  of  argument,  too  minute,  most  of 
them,  to  seem  worth  publication,  but  all  together 
forming  a  complete  whole  whose  weight  is  very 
great. 

53 


54  EVOLUTION  OF  TO-DAY. 

It  is  almost  hopeless  to  attempt  to  give  to  any 
one  not  acquainted  with  the  subject,  any  thing  like 
a  complete  understanding  of  even  the  general  bear- 
ings of  the  question.  It  is  useless  to  try  to  give 
instances,  because  they  are  significant  only  from 
their  abundance.  To  show  how  many  features  man 
has  in  common  with  the  lower  animals  ;  to  show 
how  the  abnormalities  of  his  body  are  readily  ex- 
plained by  reference  to  other  vertebrates  ;  to  mention 
the  fact  that  the  human  embryo  possesses  gill  slits 
at  the  side  of  the  neck  like  those  of  the  fish,  and 
has  a  similar  distribution  of  blood-vessels ;  to  show 
that  the  highly  developed  mouth  parts  of  the  crab 
are  simply  modifications  of  a  primitive  type  of 
appendage  existing  in  all  Crustacea;  that  there  is 
every  stage  from  a  simple  hydroid  bearing  sexual 
organs  to  a  free  swimming  jelly  fish  ;  and  to  bring 
forward  an  unlimited  number  of  other  similar  facts, 
means  nothing  to  the  general  reader,  or  indeed  to 
any  one  except  those  already  familiar  with  the  facts 
from  personal  knowledge.  Or  if  they  do  mean  any 
thing,  they  are  looked  upon  as  simple  instances  of 
the  acknowledged  fact  that  there  is  in  nature  a  pos- 
sibility of  classification,  and  that  animals  show 
homologies  with  each  other.  It  is  needless  to 
attempt  to  show  how  universal  is  this  principle  of 
homology  in  animate  nature,  for  its  existence  will 
be  everywhere  acknowledged.  The  real  question 
to  be  raised,  as  far  as  this  subject  concerns  evolution, 
is,  not  as  to  what  organs  are  homologous  in  different 
animals,  nor  as  to  what  may  be  the  true  classifica- 
tion, but  what  does  homology  mean,  and  why  should 


TWO  EXPLANATIONS  OF  CLASSIFICATION.      55 

there  be  a  true  classification  in  distinction  front  a 
false  one.  Likeness  is  always  more  difficult  to 
explain  than  unlikeness,  although  we  frequently 
think  the  contrary,  and  that  animals  should  show 
likeness  according  to  which  they  may  be  classified  is 
a  fact  requiring  explanation.  Granting  that  a  classi- 
fication exists,  and  all  of  the  above-mentioned 
classes  of  facts  follow  as  necessary  consequences ; 
still,  why  should  a  classification  and  homologies 
exist?  This  is  the  significant  question  upon  which 
the  argument  rests. 

Any  thing  can  be  classified.  Chairs  may  be  clas- 
sified into  rocking-chairs  and  stationary  chairs  ;  or 
into  walnut  chairs  and  pine  chairs  ;  or  into  cane- 
seated  chairs  and  wooden-seated  chairs.  Any  of 
these  divisions  would  be  classification,  and  any  one 
would  be  as  true  as  the  others.  But  a  long  study  of 
the  organic  world  has  shown  that  its  classification  is 
quite  different  from  such  artificial  divisions.  Natu- 
ralists have  everywhere  agreed  that  there  is  in  the 
organic  world  a  natural  classification,  a  true  classifi- 
cation in  distinction  from  hundreds  of  false  ones 
which  can  be  made.  No  such  natural  classification 
exists  among  artificial  products  nor  among  minerals, 
but  only  in  the  organic  world.  Such  a  classification 
existing  in  nature  demands  explanation. 

Two  Explanations  of  Classification, 

Practically  only  two  explanations  have  been  of- 
fered toward  the  solution  of  this  problem.  The  first 
is  the  theory  of  types  held  by  Cuvier  and  afterward 
by  Agassiz,  and  is  briefly  as  follows.  The  Creator 


56  EVOLUTION  OF  TO-DAY. 

had  in  his  mind  certain  types  in  accordance  with 
which  he  created  species.  All  animals  and  plants 
created  must  be  moulded  according  to  one  of  the 
types,  although  great  variation  could  take  place 
within  the  type,  and  never  exceeding  its  limits. 
The  type  was,  therefore,  a  purely  ideal  form  exist- 
ing only  in  the  mind  of  the  Creator.  Of  these  types 
Cuvier  recognized  four.  But  besides  the  great  types, 
it  is  necessary,  in  order  to  make  the  theory  com- 
plete, to  assume  that  each  class  of  animals  was 
made  according  to  a  sub-type,  each  order  according 
to  a  sub-sub  type,  and  so  on  for  families  and  genera. 
Individuals  could  vary  within  the  type  of  the  species, 
species  within  the  type  of  the  genus,  genera  within 
the  type  of  the  family.  The  whole  animal  and  vege- 
table kingdoms  are  thus  moulded  in  accordance 
with  many  types  and  sub-types,  each  of  which  must 
have  existed  in  the  mind  of  the  Creator  when  he 
created  species. 

Modern  scientists  are,  however,  not  satisfied  with 
this  explanation,  for  reasons  which  will  presently 
appear,  and  have  offered  evolution  as  the  explana- 
tion sought.  This  theory  claims  that  the  likenesses 
between  animals  are  due  to  descent  from  common 
ancestors  ;  that  the  well-known  principle  of  heredity, 
in  accordance  with  which  the  child  is  like  the  parent, 
is  a  sufficient  explanation  of  classification  and 
homology.  The  classification  of  organisms  is  thus 
simply  arranging  them  according  to  their  genetic 
relationship :  those  animals  showing  the  greatest 
likeness  having  the  most  recent  common  ancestor ; 
those  more  unlike  being  more  distantly  related  ; 


TWO  EXPLANATIONS  OF  CLASSIFICATION.       57 

while  the  great  types  of  Cuvier  have  had  no  com- 
mon ancestor  later  than  the  very  beginning  of  animal 
life  on  the  globe. 

It  is  very  interesting  to  compare  the  arguments 
brought  forward  by  the  last  great  exponent  of  the 
theory  of  types,  and  those  which  evolutionists  to-day 
use  in  support  of  their  own  views.  Agassiz'  "  Essay 
on  Classification,"  appearing  just  before  the  "  Origin 
of  Species,"  was  a  masterly  attempt  to  prove  the 
theory  of  types.  In  this  essay  are  brought  forward 
thirty  different  lines  of  argument,  each  of  which  was 
carefully  considered,  and  was  believed  to  be  strong 
evidence  for  the  views  held  by  the  author.  Now  an 
examination  of  these  arguments  gives  a  rather  sur- 
prising result.  Of  the  thirty  lines  of  argument,  no 
less  than  twenty-six  have  been  directly  turned  upon 
their  author,  and  are  now  used  as  arguments  in 
favor  of  evolution,  some  of  them,  indeed,  forming 
the  strongest  pieces  of  evidence  which  the  evolution- 
ist has  to  offer  to-day,  e.  g.,  the  parallel  between  em- 
bryology and  paleontology.  Of  the  other  four  points, 
one  still  remains  as  a  difficulty  for  evolution,  viz. : 
the  simultaneous  appearance  of  the  different  types 
in  the  earliest  geological  ages  ;  one  of  the  others  has 
been  disproved,  while  the  remaining  two  do  not  at 
present  seem  to  have  any  particular  significance  for 
either  side  of  the  question.  This  result,  which  must 
have  been  very  unexpected  to  Agassiz,  simply  indi- 
cates what  a  different  theory  evolution  has  been 
since  Darwin  from  what  it  was  before,  and  that  the 
theory  which  Agassiz  was  combating  was  very 
different  from  the  evolution  of  later  years.  Both 


58  EVOLUTION  OF  TO-DAY. 

Agassiz  and  Darwin  recognized  that  there  is  a  unity 
in  the  organic  world,  and  to  prove  this  unity  essen- 
tially the  same  arguments  were  used  by  both.  In 
the  interpretation  of  this  unity  only  did  they  differ. 
While  Agassiz  places  the  unity  in  the  mind  of  the 
Creator,  Darwin  finds  an  equally  intelligible  and  a 
much  more  natural  explanation  in  the  theory  of 
genetic  descent.  Agassiz'  essay  was  thus  as  strong  an 
argument  for  evolution  as  it  was  for  his  own  theory, 
although,  of  course,  he  did  not  recognize  this  fact. 

Either  of  these  theories  is  an  explanation  of  clas- 
sification, and  either  of  them  if  admitted  will  account 
for  many  or  most  of  the  facts.  It  is,  moreover,  by 
no  means  impossible  that  both  may  be  in  a  measure 
right ;  that  types  of  the  animal  kingdom  did  exist  in 
the  mind  of  the  Creator,  and  that  his  method  of  ex- 
pressing or  materializing  these  types  was  by  genetic 
descent,  or  evolution.  While  then  the  two  views  are 
not  incompatible,  we  must  recognize  that  the  first  is 
not  open  to  investigation,  since  it  lies  beyond  the 
realm  of  human  knowledge.  The  evolutionist,  more- 
over, claims  that  whatever  be  our  belief  as  to  crea- 
tion, the  facts  of  the  organic  world  are  such  as  to  in- 
dicate that  the  introduction  of  species,  families,  etc., 
into  this  world,  has  been  by  genetic  descent,  and  that 
the  history  of  the  organic  world  has  been  evolution. 
The  reasons  for  this  claim  we  must  now  examine. 

The  Relation  of  the  Various  Great  and  Small  Types 
is  Expressed  by  a  Branching  Tree-like  Structure. 

It  has  been  in  the  first  place  urged  by  those  who 
argue  for  evolution,  that  upon  the  theory  of  types 


CLASSIFICATION  A    TREE-LIKE  STRUCTURE.    59 

the  animal  kingdom  ought  to  be  arranged  in  parallel 
lines.  "  Strict  classification  of  forms  supposed  con- 
stant excludes  any  natural  relationship."  If  the 
types  were  definite  norms,  their  lowest  representa- 
tives should  be  just  as  different  from  animals  of 
other  types  as  are  the  highest.  Each  animal  would 
be  moulded  strictly  in  accordance  with  its  type,  and 
since  the  types  are  distinct,  the  different  sub-king- 
doms could  not  approach  each  other,  but  would 
remain  as  separate  parallel  lines  from  their  first  ap- 
pearance. And,  moreover,  since  to  make  the  theory 
complete  it  is  necessary  to  assume  sub-types,  the 
same  would  be  true  of  smaller  divisions,  and  there 
could  be  no  conveyance  of  lines  of  relationship 
toward  each  other,  but  they  would  remain  always 
parallel.  If,  e.  g.,  the  mammal  and  the  fish  are  dis- 
tinct creations  according  to  different  sub-types,  they 
ought  to  be  as  distinct  when  created  as  they  are  to- 
day. But  it  was  claimed  by  Darwin,  and  the  claim 
has  been  growing  in  favor  since  then,  until  it  has 
received  universal  acceptance,  that  such  is  not  the 
relation  of  the  divisions  of  the  animal  kingdom. 
There  are  no  parallel  lines,  but  all  converge  toward 
each  other  as  we  go  downward  and  backward.  The 
relation  of  the  different  groups  of  the  animal  and 
vegetable  kingdoms  is  to  be  looked  upon  in  the 
form  of  a  branching  tree,  each  sub-kingdom  repre- 
senting a  great  branch  ;  each  class,order,  family,  and 
genus  smaller  and  smaller  branches,  while  the  species 
are  simply  the  terminal  twigs  and  leaves.  The 
trunk  of  the  tree,  where  all  of  the  great  branches 
unite,  has  been  carried  farther  and  farther  back  until 


60  EVOLUTION  OF  TO-DAY. 

it  has  all  but  disappeared  in  the  dim  past,  although 
such  a  trunk  can  be  found  by  studying  embryology. 
If  this  claim  of  the  tree-like  arrangement  of  the 
animal  kingdom  be  substantiated,  it  is  proved  that 
the  old  idea  of  types  is  not  in  accordance  with  the 
facts,  while  the  theory  of  genetic  descent  is  in  exact 
accordance.  We  must,  then,  now  examine  the  evi- 
dence which  morphologists  have  brought  forward  to 
substantiate  their  claim. 

It  has  been  shown  in  the  first  place  that  if  types 
be  admitted  at  all,  more  than  four  must  be  recog- 
nized. Modern  science  has  conclusively  proved  that 
Cuvier's  Radiata  must  be  divided  into  ccelenterata 
and  echinoderms ;  that  the  Articulata  consists  of  two 
very  different  groups,  artheropoda  and  vermes ; 
and  that  one  extra  group,  the  protozoa,  is  undoubt- 
edly to  be  added.  The  sub-kingdom,  vertebrata,  is 
still  retained,  though  to  it  has  been  added  one  class 
of  animals  formerly  called  mollusks ;  while  there 
exist  some  animals  which  do  not  belong  to  any  of 
these  types  (brachiopoda,  polyzoa,  and  chaetog- 
naths).  And,  finally,  it  is  becoming  daily  more  and 
more  evident  that  the  modern  sub-kingdom,  vermes 
(part  of  Cuvier's  Articulata),  is  a  group  which  is 
made  to  contain  almost  any  animal  which  shows  no 
marked  relationship  to  others,  and  consequently  is  a 
heterogeneous  collection  of  animals  with  almost  no 
likeness  to  each  other.  And  so  in  regard  to  the 
other  sub-kingdoms.  If  we  attempt  to  define  the 
limits  of  any  of  the  so-called  types,  the  result  is  only 
confusion  and  contradiction ;  and  after  we  have 
settled  upon  a  certain  number  of  them  as  represent- 


CLASSIFICATION  A    TREE-LIKE  STRUCTURE.  6 1 

ing  the  nearest  approximation  to  the  truth,  it  be- 
comes evident  that  the  divisions  thus  recognized  have 
an  unequal  value.  Indeed,  one  of  the  best  of  modern 
scientific  books  does  not  attempt  to  arrange  the 
animal  kingdom  into  sub-kingdoms,  realizing  the 
futility  of  all  such  endeavors,  but  simply  takes  up  in 
different  chapters  animals  which  seem  to  the  author 
to  deserve  separate  rank.  No  less  than  twenty-six 
different  types  are  thus  considered,  although  their 
value  is  not  by  any  means  the  same,  the  author  rec- 
ognizing that  his  division  is  only  provisional.  The  old 
idea  of  types  has  thus  been  supplanted  by  the  more 
modern  view,  that  types  are  not  rigid  norms,  or  that 
if  they  do  exist  we  know  nothing  about  them,  not 
even  their  number,  for  the  animal  kingdom  can  be 
divided  with  almost  equal  justice  into  five,  seven, 
eleven,  or  even  more  different  groups. 

It  appears  then  that  no  rigid  lines  can  be  drawn 
separating  from  each  other  the  so-called  types.  Va- 
rious attempts  to  draw  such  lines  have  been  made. 
It  was  urged  for  a  long  time  that  no  homologies 
exist  between  members  of  the  different  types ;  that 
the  parts  of  a  vertebrate  can  be  homologous  with 
those  of  any  other  vertebrate,  but  never  with  a  mol- 
lusk  or  a  radiate.  If  this  were  true  it  would  certainly 
define  the  types.  This  subject,  therefore,  has  been 
the  scene  of  a  long  battle,  which  is  not  entirely  set- 
tled even  to-day.  It  is  now  recognized,  however, 
that  it  is  possible  to  discover  certain  homologies 
between  members  of  the  so-called  types,  though 
naturally  not  so  exact  as  between  animals  more 
closely  related.  The  wkole  series  of  homologies  is 


62  EVOLUTION  OF  TO-DAY. 

a  graded  one.  Between  man  and  his  nearest  allies, 
the  apes,  the  homology  is  very  close,  the  structure 
of  the  body  being  very  similar,  except  in  small  de- 
tails. Between  man  and  more  distant  forms,  such 
as  the  dog,  it  is  much  less  exact.  Between  man  and 
the  reptile  it  is  still  less  striking.  Between  man  and 
the  bony  fish  it  is  very  much  less  exact.  If  man  be 
compared  with  the  lowest  vertebrate  the  homologies 
to  be  found  are  confined  to  two  or  three  organs — 
the  alimentary  canal  and  the  nervous  system ;  and 
even  in  these  organs  the  differences  exceed  the 
likenesses.  And  now  if  we  go  one  step  farther  and 
attempt  to  compare  man  in  a  similar  manner  with 
some  invertebrates,  while  the  homology  is  still  less 
exact,  it  can  be  distinctly  traced.  The  nervous  sys- 
tem is  in  some  invertebrates  at  least  partly  homolo- 
gous with  that  of  man ;  and  the  alimentary  canal 
remains  the  same.  Vertebrates  and  invertebrates 
possess  a  circulatory  system  fundamentally  alike, 
and  the  excretory  system  in  almost  all  animals 
shows  a  remarkable  resemblance.  Finally,  if  we 
extend  our  comparison  to  the  embryonic  stages  we 
can  find  very  abundant  evidence  that  homologies 
do  exist  between  all  animals.  The  young  mollusk, 
the  young  worm,  the  young  polyzoan,  in  a  stage 
called  the  trochosphere  show  a  likeness  amounting 
almost  to  identity ;  and  if  we  take  a  still  younger 
stage,  we  find  all  types  possessing  a  structure  practi- 
cally the  same.  If  now  we  take  these  identical 
embryonic  stages  as  a  guide,  there  is  no  longer  any 
difficulty  in  drawing  homologies  between  the  adults 
of  all  animals.  While  this  is  everywhere  recog- 


CLASSIFICATION  A  TREE-LIKE   STRUCTURE.      63 

nized,  it  must  be  acknowledged  that  different  mor- 
phologists  have  not  reached  the  same  conclusions  as 
to  these  homologies  in  all  cases. 

But  it  is  undoubtedly  a  fact  that  to  a  certain  ex- 
tent homologies  can  be  traced  between  animals  as 
widely  separated  as  the  so-called  types.  It  is 
further  a  significant  fact  that  these  homologies  are 
most  noticeable  when  the  lower  members  of  the  dif- 
ferent types  are  compared  with  each  other  ;  in  other 
words,  the  types  approach  each  other  at  the  bottom. 
The  lowest  vertebrates  approach  much  more  closely 
to  the  invertebrates  than  do  the  higher  members  of 
this  group  ;  so  close  indeed  that  in  some  cases  low 
vertebrates  have  been  classed  with  one  or  another 
of  the  invertebrate  classes.  All  of  this  would  of 
course  naturally  follow  from  the  descent  theory ; 
for  the  lower  members  are  nearer  to  the  supposed 
common  ancestor.  And  this  theory  would  lead  us 
to  expect  that  there  might  be  some  animals  inter- 
mediate between  the  great  types,  which  represent 
their  common  starting-point.  Very  careful  search 
after  such  forms  has  been  made,  and  certain  small 
circumscribed  groups  have  been  found,  consisting 
perhaps  of  only  a  single  species,  which  show  so 
many  general  likenesses  that  they  do  not  seem  to 
belong  anywhere,  but  have  been  changed  about 
from  place  to  place,  now  with  one  class  of  animals 
and  now  with  another,  until  it  has  been  assumed  by 
the  advocates  of  the  evolution  hypothesis  that  they 
form  connecting  links  between  the  great  types. 
This  point  has  been  strongly  emphasized  by  some 
naturalists,  and  would  be  highly  important  if  true; 


64  EVOLUTION  OF  TO-DAY. 

but  it  has  proved  upon  close  examination  to  be  in 
most  cases  a  delusion.  Most  of  these  animals  have 
been  found  to  be  simple  but  somewhat  modified 
representatives  of  one  of  the  large  classes,  and. not 
connecting  links  between  them.  For  instance:  the 
Ascidians  have  been  classed  in  many  places,  and 
finally  when  the  discoveries  of  a  Russian  naturalist 
showed  their  vertebrate  affinities,  they  were  imme- 
diately hailed  as  connecting  links  between  the  ver- 
tebrates and  some  group  of  invertebrates,  probably 
the  mollusks.  But  a  more  careful  study  in  the  last 
few  years  has  shown  that  the  Ascidians  are  true  ver- 
tebrates, degenerate  forms  it  is  true,  but  still  un- 
questionably vertebrates,  and  not  in  any  sense  con- 
necting links  as  was  at  first  hoped.  Another  animal, 
the  far-famed  Amphioxus,  held  its  rank  as  such  a 
connecting  link  for  a  longer  period  ;  but  this  too  is 
now  seen  to  be  a  very  simple  and  degenerate  verte- 
brate. And  so  in  general  the  connecting  links  be- 
tween the  sub-kingdoms  and  often  too  between  the 
smaller  groups,  prove  upon  examination  to  be  modi- 
fied members  of  one  or  the  other  of  the  groups  which 
they  are  supposed  to  unite. 

And  indeed  connecting  links  are  very  little  looked 
for  now  ;  for  it  is  recognized  that  we  cannot  expect 
to  find  them  living  to-day.  The  animals  which  ex- 
ist to-day  are  not  in  direct  line  with  each  other,  but 
are  the  separate  terminations  of  lines  converging 
toward  each  other  in  the  past.  The  common  ances- 
tors representing  the  points  of  union  of  these  lines 
were  animals  which  have  lived  in  the  distant  past, 
and  as  a  rule  they  will  have  disappeared.  Perhaps 


CLASSIFICATION  A   TREE-LIKE   STRUCTURE.   6$ 

in  the  case  of  closely  related  species,  connecting 
links  may  be  found,  for  they  are  of  so  recent  origin 
that  the  common  form  from  which  they  have  de- 
scended may  not  in  all  cases  have  become  extinct. 
But  when  a  wide  difference  exists,  such  as  that  be- 
tween the  different  sub-kingdoms,  the  common  point 
of  union  is  so  far  back  in  the  past  that  the  existence 
of  connecting  links  to-day  would  be  a  marvellous 
thing.  Such  forms  must  have  lived  at  the  very  be- 
ginning of  or  even  before  the  Silurian  age,  and  if 
they  were  found  to-day  it  would  indicate  a  survival 
through  periods  longer  than  any  form  has  been 
known  to  exist.  They  would  thus  be  obstacles 
rather  than  arguments  for  the  descent  theory.  And 
to  take  another  somewhat  different  case  :  the  de- 
mand for  the  "  missing  link  "  between  man  and  the 
ape,  at  one  time  so  strenuously  urged,  has  been 
nearly  abandoned,  for  it  is  recognized  that  the  very 
fact  that  man  has  arisen,  necessitates  the  disappear- 
ance of  his  primitive  ancestor. 

But  evidently  these  links  must  have  existed  at 
some  time,  if  not  to-day,  yet  in  the  past.  We 
ought  to  expect,  therefore,  that  the  various  types, 
although  not  connected  by  living  forms,  are  con- 
nected by  fossil  forms.  This  question  is  treated 
more  at  length  in  another  chapter,  and  it  is  here 
only  necessary  to  say  that  even  by  fossils  the  sub- 
kingdoms  are  not  connected.  No  fossils  have  been 
discovered  which  unite  the  sub-kingdoms  with  each 
other,  the  earliest  animals  known  belonging  to  one 
or  another  of  the  types ;  a  fact  which  forms  one  of 
the  chief  difficulties  which  evolution  has  to  meet. 


66  EVOLUTION  OF  TO-DAY. 

But  although  this  is  true,  fossils  do  enable  the 
naturalist  to  classify  all  divisions  within  the  sub- 
kingdoms,  in  a  tree-like  arrangement,  by  presenting 
numerous  links.  To  consider  briefly  an  example. 
The  vertebrates  to-day  consist  of  many  widely  separ- 
ated orders  unconnected  by  intermediate  forms. 
But  fossil  vertebrates  are  very  numerous,  and  in  a 
great  many  cases  fall  into  gaps  between  existing 
orders.  The  Ungulates,  the  Proboscidea,  the  Hyra- 
coidea,  and  the  Sirenia,  can  all  be  traced  backwards 
by  converging  lines,  until  they  meet  at  a  point  rep- 
resented by  a  mammal  of  the  lower  tertiary.  The 
Cetacea,  Carnivora,  and  Rodents  in  like  manner 
approach  each  other.  The  birds  and  reptiles  ap- 
proach ancient  Cretaceous  forms,  which  represent 
their  common  point  of  origin,  although  the  record 
is  less  perfect  here  than  in  the  case  of  mammals. 
Beyond  the  Cretaceous  the  record  is  so  incomplete 
as  to  make  the  history  less  positive :  but  the  evi- 
dence, as  far  as  collected,  points  to  the  union  of  all 
the  classes  of  vertebrates  in  some  ancient  fish-like 
form  which  lived  in  the  Silurian  age.  In  no  case  is 
the  record  of  these  lines  complete  ;  even  in  the 
most  perfect  instances  there  are  many  gaps.  But 
fossils  do  show  many  of  the  intermediate  links  for 
which  we  are  searching,  and  beyond  a  shadow  of 
doubt  the  paleontological  record  indicates  that  the 
classification  of  the  animals  within  any  given  sub- 
kingdom  is  such  as  is  represented  by  the  tree-like 
arrangement  of  expressing  relations. 

In  order  to  complete  the  evidence  that  this  repre- 
sents the  true   classification    of   the   whole   animal 


CLASSIFICATION  A   TREE-LIKE   STRUCTURE.   6/ 

kingdom,  it  is  necessary  to  show  that  the  sub-king- 
doms— the  types  of  Cuvier — are  themselves  con- 
nected at  the  bottom.  This,  we  have  seen,  cannot 
be  done  by  living  animals  nor  by  fossils,  but  a  third 
source  of  evidence  makes  it  possible.  The  subject 
of  embryology  is  also  reserved  for  a  later  chapter. 
The  last  few  years'  study  in  this  subject  has  shown 
that  there  is  no  lack  of  evidence  that  the  great 
types  can  be  united  in  some  common  ancestor  of 
ancient  times.  Embryology  enables  us  to  connect 
the  different  sub-kingdoms  with  each  other  at  a  com- 
mon starting-point,  and  to  trace  this  common  form 
still  further  back  toward  the  simplest  animal.  And 
thus  our  tree  of  classification  has  a  trunk.  If  we 
take  any  two  animals  and  trace  their  embryology 
backwards,  we  find  them  becoming  more  and  more 
alike,  until  they  finally  merge  in  a  common  form  in 
the  early  part  of  their  history. 

And,  finally,  it  must  be  noticed  that  not  only  do 
the  sub-kingdoms  approach  each  other  and  unite  at 
a  common  point,  but  the  two  kingdoms  of  organic 
life,  animals  and  plants,  in  a  like  manner,  converge. 
So  evident  is  this,  that  it  has  led  to  the  establish- 
ment of  a  third  kingdom  of  organisms,  neither 
plants  nor  animals,  but  representing  the  union  of 
the  two.  This  kingdom,  called  the  Protista,  con- 
tains a  number  of  microscopic  forms.  Although 
the  advisability  of  forming  such  a  kingdom  is  very 
questionable,  the  very  fact  that  it  has  been  done 
by  some  naturalists  is  sufficient  indication  that  the 
animal  and  vegetable  kingdoms  do  approach  each 
other  at  the  bottom. 


68  EVOLUTION  OF  TO-DAY. 

The  Value  of  this  Tree-like  Classification. 
When  now  this  sort  of  classification,  as  taught  by 
anatomy,  paleontology,  and  embryology,  with  its 
implied  theory  of  genetic  descent,  comes  to  be  ap- 
plied to  interpreting  the  existing  animal  kingdom, 
it  is  found  that  a  wonderful  light  is  thrown  upon 
the  whole  subject.  This  conception  has,  of  course, 
gradually  grown  out  of  the  older  one,  and  has  only 
step  by  step  taken  its  place.  The  nominal  relation- 
ship of  animals  remains,  therefore,  much  the  same 
as  it  has  always  been,  although  many  are  now 
classed  together  which  were  previously  thought  to 
be  separate,  and  many  are  now  widely  separated 
which  were  previously  thought  to  be  closely  re- 
lated, and  many  animals  whose  relationship  was 
formerly  a  complete  mystery,  are  now  easily  under- 
stood. For  the  term  relation  has  now  a  meaning, 
and  it  is  seen  that  an  animal  may  be  a  vertebrate, 
and  still  show  some  relationship  to  other  types.  To 
use  the  words  of  a  modern  writer :  "  All  the  enigmas 
of  structure  become  resolved  ;  representative  and 
aberrant,  progressive  and  degraded,  synthetic  and 
isolated,  persistent  and  prophetic  types  no  longer 
baffle  comprehension."  It  becomes  evident  that 
there  is  a  real  meaning  to  the  term  natural  classifica- 
tion, a  fact  long  since  recognized,  but  not  understood. 
We  can  understand  now  why  it  is  that  organs  of 
the  least  importance  to  the  animal  are  usually  of  the 
greatest  weight  in  classification ;  for  organs  of  no 
functional  importance  can  only  be  explained  by  in- 
heritance from  some  ancestor  in  which  they  were 
useful ;  and  since  they  are  of  no  present  value,  they 


CLASSIFICATION  A   TREE-LIKE   STRUCTURE.  69 

will  not  be  modified  to  suit  the  surroundings,  but 
will  (until  they  finally  disappear)  retain  something 
of  their  primitive  structure.  The  common  posses- 
sion of  these  organs  is,  therefore,  an  evidence  of 
common  descent,  and  since  they  are  slightly  modi- 
fied, they  will  be  the  most  important  features  for  de- 
termining relations.  It  is  seen,  on  the  other  hand, 
why  it  is  that  adaptive  likeness,  such  as  that  between 
the  fish  and  the  whale,  is  of  no  use  in  classification. 
It  becomes  evident  why  indeed  it  is  that  the  rudi- 
mentary teeth  in  the  jaws  of  the  embryo  whale  are 
of  more  importance,  as  indicating  relationship,  than 
the  whole  of  the  remarkable  resemblance  to  the 
fish.  Nearly  all  of  the  somewhat  intricate  princi- 
ples of  classification,  arrived  at  originally  from 
purely  empirical  grounds,  can  now  be  elucidated 
by  a  clear  understanding  of  this  principle  and  expla- 
nation of  classification.  In  short,  it  becomes  clearly 
evident  that  the  true  classification  of  the  organic 
world  is  not  in  isolated  parallel  lines,  as  was  pre- 
viously believed,  but  after  the  form  of  a  branching 
tree.  This  sort  of  classification  may  therefore  be 
looked  upon  as  definitely  settled  by  the  combined 
aid  of  paleontology,  embryology,  and  the  compara- 
tive study  of  adult  anatomy,  although  it  was  origi- 
nally the  result  of  the  conception  of  evolution. 

Although  this  conclusion  may  be  regarded  as  set- 
tled, it  of  course  by  no  means  proves  the  descent  the- 
ory. What  it  does  prove  is  that  the  facts  are  in 
harmony  with  the  descent  theory  and  are  not  in  har- 
mony with  the  older  idea  of  types.  It  is  perfectly 
possible  that  the  idea  of  types  and  of  special  creation 


7O  EVOLUTION  OF  TO-DAY. 

can  be  modified  so  as  to  be  in  accordance  with  all 
of  the  facts  mentioned.  The  force  of  the  evolution 
argument  here  is  not  in  the  impossibility  of  making 
some  other  theory  to  fit  the  facts,  but  in  the  fact 
that  (i)  all  other  theories  are  supernatural  explana- 
tions rather  than  natural,  and  (2)  that  they  are 
unnecessary,  for  the  simple  theory  of  descent  is 
entirely  sufficient  to  explain  the  classification  of  the 
organic  world. 

Application  of  the  Theory  to  the  Explanation  of  Ho- 
mology — Homology  in  General —  Serial  Homology. 

Let  us  now  turn  to  some  of  the  minor  applica- 
tions of  the  argument  and  see  how  the  theory 
explains  some  special  features.  First  let  us  notice 
the  explanation  of  homology  in  general.  Homolo- 
gous organs  are  those  whose  structures  are  alike, 
though  their  functions  may  be  entirely  different ;  for 
instance,  the  short  useless  tail  of  the  hog  and  the 
highly  developed  prehensile  tail  of  the  monkey  are 
homologous ;  or  the  arm  of  a  man  and  the  wing  of 
a  bird.  Analogous  organs  are  those  whose  func- 
tions are  alike,  though  their  structures  may  be  very 
different ;  as  the  bird's  wing  and  the  butterfly's 
wing.  Analogous  likenesses  are  plainly  of  second- 
ary importance,  existing  because  the  organs  in 
question  have  similar  functions.  Homologous  like- 
ness is  of  much  more  significance,  since  it  exists  in 
spite  of  differences  in  function  and  clearly  indicates 
some  fundamental  likeness  between  animals.  The 
whole  subject  of  comparative  anatomy  or  morphol- 
ogy is  the  study  of  homologies  of  structure.  When 


HOMOLOGY.  71 

two  animals  somewhat  closely  related  are  compared, 
let  us  say  the  dog  compared  with  man,  it  is  found 
that  they  are  built  upon  exactly  the  same  plan,  and 
can  be  compared  with  each  other  bone  for  bone  and 
muscle  for  muscle.  The  more  thorough  be  the 
comparison  the  greater  appears  the  likeness,  for  the 
very  abnormalities  strengthen  it.  Muscles  occa- 
sionally found  in  one  are  universally  present  in  the 
other  ;  and  so  with  special  protuberances  of  bones, 
with  nerves,  and  with  almost  every  other  feature ; 
everything  shows  that  there  is  a  complete  homology 
between  the  bodies  of  different  vertebrates,  and  it  is 
the  duty  of  the  anatomist  to  discover  these  homolo- 
gies. 

What  is  the  exact  answer  which  the  theory  of 
evolution  will  give  to  the  question  of  the  real 
explanation  of  this  homology?  A  man's  arm  and  a 
bird's  wing  are  organs  with  totally  different  func- 
tions and  very  different  in  shape  ;  yet  in  spite  of  this 
difference  they  are  fundamentally  alike  in  their 
muscles  and  bones.  The  theory  of  evolution  will 
say  that  this  likeness  is  due  to  the  fact  that  both 
man  and  bird  have  descended  from  a  common 
ancestor,  living  long  ago,  which  possessed  an 
appendage,  neither  an  arm  nor  a  leg,  but  containing 
the  fundamental  structure  of  both,  /.  e.,  the  features 
which  they  possess  in  common.  The  descendants 
of  this  ancestor  in  the  course  of  many  generations 
became  modified  in  two  directions  and  their  appen- 
dages were  correspondingly  modified.  On  the  one 
hand  the  descendants  became  flying  animals  and 
the  anterior  limb  was  developed  into  a  wing,  retain- 


72  EVOLUTION  OF  TO-DAY, 

ing,  of  course,  its  fundamental  features,  but  chan- 
ging its  shape  to  suit  the  change  in  function.  On 
the  other  hand,  the  descendants  remaining  terres- 
trial, the  limb  became  a  grasping  organ,  likewise 
retaining  its  fundamental  structure.  Thus  the  the- 
ory of  descent  with  modification  explains  both  the 
similarities  and  the  differences  between  homologous 
organs,  the  former  being  due  to  inheritance  and  the 
latter  to  variation.  And  as  far  as  instances  of  this 
kind  are  concerned  the  explanation  is  certainly- 
sufficient. 

But  there  is  another  very  different  class  of  homol- 
ogies  which  cannot  be  thus  explained.  What  can 
be  said  of  the  homology  which  exists  between  the 
arm  and  leg  of  a  man,  between  the  wing  and  leg  of 
a  bird,  between  the  members  of  the  long  series  of 
legs  of  the  lobster — in  short,  between  all  sorts 
of  serial  organs  ?  Here  is  a\  homology  as  exact 
as  that  in  the  case  considered  above.  Every  bone 
in  the  arm  has  its  homologue  in  the  leg  ;  every  ap- 
pendage of  the  lobster  is  strictly  comparable,  joint 
by  joint,  with  all  the  others.  Indeed,  the  exactness 
of  this  serial  homology  is  frequently  more  complete 
than  that  of  the  general  homologies  above  re- 
ferred to,  and  it  is  very  evident  that  this  type  of 
homology  requires  an  explanation  just  as  truly  as 
did  the  first.  But  the  explanation  given  to  the  first 
case  will  not  apply  here.  Let  us  see  what  would 
be  the  result.  Using  the  above  explanation,  we 
should  say  that  the  arm  and  leg  owe  their  likeness 
to  the  fact  that  they  have  both  descended  from 
a  common  ancestor,  which  possessed  the  funda- 


HOMOLOGY.  73 

mental  features  of  both.  Now  this  means  absolutely 
nothing,  for  it  necessitates  the  assumption  that 
there  once  existed  a  vertebrate  with  only  one  pair 
of  appendages  ;  and  no  one  has  the  hardihood  to 
make  such  a  claim.  In  such  serial  appendages  we 
have,  therefore,  an  homology  which  is  not  open  to 
the  explanation  given  to  homologies  in  general,  and 
the  fact  that  the  explanation  will  not  apply  here 
makes  it  at  least  a  legitimate  question  whether  it  is 
sufficient  in  the  other  cases.  At  all  events,  unless 
some  other  way  of  accounting  for  serial  homologies 
can  be  discovered,  it  can  hardly  be  claimed  that  the 
reason  for  homologies  is  understood.  The  whole 
argument  for  descent,  derived  from  comparative 
anatomy,  is,  in  a  measure,  weakened  unless  these 
cases  be  met. 

Spencer  has  attempted  to  answer  this  question  in 
accordance  with  the  theory  of  evolution.  He 
would  distinguish  two  sorts  of  serial  homologies 
which  have  had  different  origins.  The  first  is  that 
which  is  found  in  Crustacea  and  other  animals, 
where  the  whole  body  consists  of  a  series  of  equiva- 
lent segments,  each  having  essentially  the  same 
parts.  This  sort  of  segmentation  has  arisen,  accord- 
ing to  Spencer,  by  multiple  division.  Many  low 
animals  possess  the  power  of  dividing  into  two 
parts,  each  of  which  is  like  the  other.  Every  organ 
shares  in  this  division.  If  now,  as  frequently  is  the 
case,  these  two  segments,  instead  of  completely  sep- 
arating from  each  other,  remain  connected  after  the 
division  is  nearly  complete,  we  should  have  a  com- 
pound animal  of  two  segments,  in  which  every  part 


74  EVOLUTION  OF  TO-DAY. 

is  duplicated.  Supposing  this  division  to  continue, 
we  should  soon  get  a  chain  of  individuals  which 
grows  longer  and  longer,  and  if  the  segments  re- 
mained connected,  the  result  would  be  a  segmented 
animal,  each  segment  of  which  is  homologous  with 
all  the  others,  for  the  simple  reason  of  descent. 
The  serial  homology  of  the  appendages  of  such  ani- 
mals is,  therefore,  explained  in  a  manner  quite  sim- 
ilar to  that  of  the  first  class.  Whether  this  theory 
is  correct,  is  not  definitely  agreed  upon  by  natural- 
ists. It  is  true  that  such  a  division  does  take  place 
in  many  low  animals.  But  it  is  also  true  that  there 
is  no  tendency  shown  to  form  thus  single  segmented 
animals,  but  rather  chains  of  independent  individu- 
als ;  and  further,  the  embryological  evidence  derived 
from  Crustacea  is  opposed  to  the  view. 

But  whether  this  theory  of  Spencer  be  true  or  not, 
does  not  materially  affect  the  argument  we  are  con- 
sidering, for  it  will  not,  does  not,  apply  to  the  homol- 
ogy of  the  four  appendages  of  vertebrates.  If  ever 
the  vertebrates  were  derived  from  the  division  of  a 
primitive  unsegmented  animal,  as  above  suggested, 
it  was  very  long  ago,  in  fact  before  the  animals  pos- 
sessed bones  at  all.  Even  supposing  that  the  ap- 
pendages did  originally  owe  their  likeness  to  such 
descent,  the  homologies  between  the  bones  which 
have  since  appeared  must  be  a  later  acquired  fea- 
ture. The  appendages  must  have  grown  alike. 
Moreover,  embryology  has  shown  that  the  earliest 
vertebrate  appendages  were  very  unlike  the  leg  or 
arm  of  man,  and  this  is  another  proof  of  the  second- 
ary character  of  their  present  homology.  Indeed, 


HOMO  LOGY.  75 

Spencer  does  not  attempt  to  apply  his  previous  ex- 
planation here.  He  thinks  that  the  segmentation 
of  vertebrates,  /.  e.,  the  division  of  the  spinal  column 
into  vertebrae,  arose  as  the  result  of  strains.  Origi- 
nally the  vertebrate  was  unsegmented,  but  in  bend- 
ing its  body  from  side  to  side  in  locomotion  through 
the  water,  its  spinal  column  became  divided  by  the 
action  of  the  simple  mechanical  force.  But  with 
this  understanding  of  the  segmentation,  the  explan- 
ation of  the  homology  between  the  leg  and  arm  is 
lost.  Spencer  simply  says  that  this  homology  is 
due  to  like  conditions  acting  on  the  two  appendages. 
But  plainly  we  are  no  better  off  than  we  were  to 
start  with,  when  we  remember  that  similar  condi- 
tions do  not  always  produce  the  same  results,  and 
that  almost  everywhere  can  be  found  instances 
where  the  same  structure  is  preserved  in  spite  of 
different  conditions.  It  is  palpable  that,  when 
Spencer  tries  to  account  for  serial  homology  in  ver- 
tebrates by  likeness  of  conditions,  he  has  simply 
abandoned  the  question  altogether. 

But,  moreover,  we  have  absolute  proof  that  this 
sort  of  homology  is  due  to  some  internal  cause  rather 
than  external  conditions.  Many  abnormalities  of 
structure  show  this  :  instances  where  extra  digits 
occur  on  both  hands  and  feet,  or  the  absence  of  the 
same  digit  on  both  hands  and  feet ;  instances  of 
both  hand  and  foot  being  similarly  affected  by 
peculiar  diseases  ;  the  development  on  the  feet  of 
birds  of  wing  feathers  like  those  of  the  anterior 
appendage.  Enough  cases  of  this  kind  are  known 
to  make  it  plain  that  there  is  some  sort  of  internal 


76  EVOLUTION  OF  TO-DAY. 

connection  between  serially  homologous  organs. 
Since,  then,  the  likeness  of  these  appendages  cannot 
be  due  to  inheritance  as  commonly  understood,  and 
since  such  cases  as  those  just  given  indicate  some 
intimate  internal  connection  between  them,  it  is 
evident  that  the  theory  of  descent  will  not  account 
for  serial  homology.  It  is  necessary  to  admit,  un- 
less some  further  explanation  can  be  found,  that 
homology  does  not  prove  descent. 

One  other  way  out  of  the  difficulty  has  been  sug- 
gested, still  in  accordance  with  the  theory  of  descent, 
though  applied  in  a  very  different  line.  This  sug- 
gestion, first  advanced  by  Darwin,  asks  if  it  is  not 
possible  to  turn  to  the  developing  ovum  for  assist- 
ance, and  suppose  that  the  internal  bond  of  like- 
ness may  be  due  to  the  fact  that  the  parts  in 
question  are  derived  from  similar  parts  of  the 
ovum.  The  first  change  which  takes  place  in  the 
developing  ovum,  is  its  division  into  a  number  of 
segments  or  cells.  After  this  division  has  continued 
for  some  time,  until  the  cells  are  quite  numerous, 
certain  cells  are  set  apart  to  become  developed  into 
certain  parts  of  the  adult.  Now  we  can  assume 
that  one  of  these  cells  is  destined  to  form  the  four 
appendages.  This  cell  goes  on  dividing,  and  the 
resulting  cells  are  moulded  into  the  form  of  the 
legs  and  arms.  It  is  easy  to  see,  therefore,  that  the 
leg  and  arm  would  show  a  tendency  to  develop  in 
similar  directions,  since  they  have  descended  from 
the  same  cell  of  the  embryo.  Serial  homology  of 
all  sorts  thus  receives  an  explanation  compatible 
with  that  given  to  the  more  general  cases.  Every 


HOMOLOGY.  77 

instance  of  homology  is  due  to  descent  from  a 
common  ancestor,  but  when  the  organs  compared 
are  upon  different  individuals  the  common  ancestor 
was  a  remote  independent  animal,  and  when  the 
organs  compared  are  upon  the  same  individual  the 
common  ancestor  is  a  simple  embryonic  cell  with 
no  appendages  but  with  power  to  produce  them. 
The  likeness  between  the  man's  arm  and  the  bird's 
wing  is  due  to  descent  from  an  ancient  intermediate 
ancestor,  that  possessed  an  appendage  with  the 
fundamental  structure  of  both  wing  and  arm.  Man's 
leg  and  arm  owe  their  likeness  to  descent  from  a 
certain  cell,  arising  from  the  ovum,  which  has  given 
origin  to  both. 

This  idea  has  been  too  little  discussed  to  justify 
any  conclusion  as  to  its  adequacy  to  meet  the  ques- 
tion, for  indeed  it  has  been  hardly  more  than  sug- 
gested by  one  or  two  writers.  There  is  some 
embryological  evidence  in  its  favor,  though  as  yet 
not  very  extensive.  It  is  certainly  an  internal  con- 
nection which  many  facts  demand,  and  will  enable 
us  to  understand  why  the  two  arms  and  two  legs 
are  liable  to  similar  diseases,  or  why  abnormalities 
occurring  in  one  would  not  be  unlikely  to  occur  in 
all  the  others.  Because  any  influence  acting  on  the 
embryonic  cell  would  affect  all  appendages  alike,  it 
would  readily  account  for  serial  abnormalities  of 
such  organs,  of  which  numerous  instances  occur. 
Whether  it  is  sufficient  to  explain  the  exact  homolo- 
logies  so  noticeable  in  serial  organs  is  not  quite  so 
clear.  But  admitting  this  as  a  partial  explanation, 
we  introduce  a  new  factor  into  our  theory  of  descent, 


78  EVOLUTION  OF  TO-DAY. 

which  is  called  embryonic  or  ontogenetic  descent. 
And  this  is  a  factor  of  which  almost  nothing  is 
known,  and  whose  limits  are  as  yet  undrawn.  One 
naturalist,  as  will  appear  later,  is  inclined  to  make 
this  the  all-important  factor  in  heredity.  But  we 
know  too  little  of  the  real  value  of  this  hypothesis  to 
justify  us  as  yet  in  admitting  that  it  is  sufficient  to 
clear  up  the  vexed  problem  of  serial  homology. 
Evidently  this  new  factor  will  not  explain  homologies 
between  different  animals,  any  more  than  the 
ordinary  theory  of  descent  will  account  for  serial 
homology,  although  both  are  explained  by  descent. 
If  we  can  accept  this  theory  the  descent  hypothesis 
becomes  logical  as  far  as  homologies  are  concerned. 
If  not,  we  must  wait  for  another  ;  at  best,  we  must 
admit  that  the  subject  is  still  a  perplexing  one. 

Rudimentary  Organs. 

An  important  feature  in  connection  with  the  classi- 
fication of  animals  and  plants,  is  the  series  of  organs 
known  as  rudimentary  organs.  They  have  always 
been  an  object  of  interest,  for,  utterly  functionless, 
their  presence  seems  entirely  unaccounted  for  unless 
they  are  assumed  to  be  rudiments  of  organs  pre- 
viously of  value.  Every  one  is  acquainted  with 
examples.  The  coccyx  of  the  human  skeleton  repre- 
sents the  tail  of  other  mammals  ;  the  so-called  splint 
bones  of  the  horse's  feet  are  the  remains  of  the  lost 
fingers  and  toes  ;  the  rudimentary  legs  of  the  boa- 
constrictor,  which  do  not  protrude  through  the  skin  ; 
the  rudimentary  teeth  in  the  whale,  which  never 
pierce  the  jaw  so  as  to  become  in  the  slightest 


RUDIMENTARY  ORGANS.  79 

degree  functional;  the  gill-slits  in  the  embryo  chick; 
the  aborted  pistils  found  in  staminate  flowers ;  all 
these  and  numerous  other  instances  will  occur  as 
illustrations  of  rudimentary  organs.  All  of  these  struc- 
tures are,  without  the  slightest  question,  homolo- 
gous with  similar  structures  well  developed  and 
functional  in  other  animals  and  plants.  They  are 
of  no  use  to  their  possessors ;  they  may  be  widely 
distributed,  and  yet  very  variable,  being  found  al- 
most exactly  alike  in  distinctly  related  species,  while 
of  two  closely  related  species,  one  may  possess  them 
and  the  other  have  almost  no  trace  of  them.  Fre- 
quently they  are  of  the  greatest  value  in  classifica- 
tion. They  must  be  comprehended  in  any  explana- 
tion of  the  organic  world,  and  no  theory  of  classifi- 
cation can  be  for  a  moment  entertained,  which  does 
not  have  its  explanation  of  these  organs. 

The  theory  of  types  meets  the  question  in  a 
manner  which  at  first  sight  seems  to  be  intelligible. 
Animals  are  built  according  to  certain  plans,  and  it 
is  necessary,  in  order  that  the  plan  be  complete,  to 
have  all  its  parts  represented.  For  symmetry  of  plan, 
therefore,  all  of  the  usual  parts  must  be  present,  but 
since,  in  many  cases  owing  to  different  habits,  some 
of  them  may  be  useless,  they  are  quite  naturally 
permitted  by  the  designer  to  be  rudimentary.  But 
aside  from  the  fact  that  the  whole  idea  of  types  is 
unsatisfactory,  it  is  evident  that  in  this  case  it  is  in- 
consistent with  itself.  If  all  closely  related  animals 
were  thus  supplied  with  the  requisite  rudimentary 
organs,  this  explanation  might  do,  but  where  one 
animal  possesses  them  and  another  almost  like  it  in 


80  EVOLUTION  OF  TO-DAY. 

other  respects  possesses  them  not,  the  idea  of  types 
becomes  plainly  inadequate.  It  may  be  said  that 
the  boa-constrictor  possesses  the  rudimentary  legs 
that  the  vertebrate  type  may  be  complete,  but  why 
are  they  wanting  in  other  snakes  ?  No  intelligible 
reason  can  be  given  why  the  type  should  be  adhered 
to  in  one  case  and  not  in  another.  Here  again  we 
find  the  theory  of  types  lacking. 

The  theory  of  descent  has  a  better  explanation, 
though  it  is  not  in  all  respects  satisfactory  as  yet. 
In  this  theory  it  is  necessary  to  distinguish  two 
classes  of  rudimentary  organs,  aborted  organs,  and 
nascent  organs. 

Aborted  Organs. 

Aborted  or  atrophied  organs  are,  according  to 
evolution,  actual  remnants  of  organs,  which  were 
functional  at  one  time  in  the  history  of  the  ancestors 
of  the  animals  now  possessing  them  as  rudiments  ; 
but  which,  on  account  of  some  change  in  the  habits 
of  the  animal,  became  no  longer  useful,  and  conse- 
quently by  disuse  gradually  became  smaller  until 
they  are  finally  simple  rudiments.  The  ancestors  of 
the  boa-constrictor  were  animals  which  in  common 
with  all  other  reptiles  possessed  legs  ;  but  this 
animal,  from  some  change  in  its  environment,  ac- 
quired creeping  habits,  and  its  legs  were  no  longer 
used.  Through  disuse  they  began  to  atrophy,  and 
finally  nothing  remains  of  them  except  the  rudi- 
ments now  found.  In  most  snakes  they  have  com- 
pletely disappeared,  but  here,  for  some  reason,  per- 
haps they  were  used  for  a  longer  period  than  in 


ABORTED   ORGANS.  8 1 

other  cases,  they  have  not  totally  disappeared,  but 
remain  as  rudiments.  The  splint  bones  of  the 
horse's  foot,  as  abundantly  proved  by  fossils,  are 
remnants  of  toes,  formerly  well  developed  and  func- 
tional in  the  horse  family,  but  which  have  become 
useless  and  consequently  reduced.  Of  the  five  toe? 
which  were  formerly  present,  two  have  completely 
disappeared,  two  remain  as  rudimentary  splint  bones, 
while  the  fifth  is  well  developed  and  functional. 
And  similarly  through  the  simple  influence  of  dis- 
use nearly  all  cases  of  atrophied  organs  are  simply 
and  naturally  accounted  for. 

But  this  explanation,  though  unquestionably  su- 
perior to  the  other,  is  not  yet  quite  satisfactory,  and 
meets  difficulties  in  at  least  two  points.  First,  it 
will  not  explain  all  rudimentary  organs.  Each  sex 
possesses  rudiments  of  organs  found  in  the  other. 
The  mammae  on  the  breasts  of  the  male  mammal 
are  truly  rudimentary  organs,  and  their  presence 
can  hardly  be  explained  by  inheritance.  This  dif- 
ficulty is  quite  similar  to  the  one  considered  above 
in  regard  to  serial  homology.  We  can  hardly  sup- 
pose that  the  male  mammal  ever  possessed  mammae, 
which  through  disuse  have  become  aborted,  although 
even  this  position  is  held  by  some  naturalists,  who 
instance  the  fact  that  it  is  the  male  in  many 
species  who  cares  for  the  young.  But  this  hypoth- 
esis will  not  be  received  as  an  answer  by  many  ;  and 
we  must  admit  that  such  rudimentary  organs  are 
unexplained,  unless  we  say  that  one  sex  has  a  tend- 
ing to  inherit  the  characteristics  of  the  other  sex. 
A  second  difficulty,  somewhat  more  serious,  is  to 


82  EVOLUTION  OF  TO-DA  F. 

understand  how  these  organs  could  have  become  so 
much  aborted  by  simple  disuse ;  or  even  more,  to  see 
how  they  could  have  disappeared  completely.  Dar- 
win has  recognized  the  difficulty.  "  After  an  organ 
has  ceased  being  used,  and  has  become  in  conse- 
quence much  reduced,  how  can  it  be  still  further  re- 
duced in  size  until  the  merest  vestige  is  left ;  and 
how  can  it  be  finally  quite  obliterated  ?  It  is 
scarcely  possible  that  disuse  can  go  on  producing 
any  further  effect  after  the  organ  has  once  been 
rendered  functionless.  Some  additional  explanation 
is  here  requisite,  which  I  cannot  give."  From  this 
passage  it  is  evident  that  the  theory  of  descent,  at 
least  as  understood  by  Darwin,  has  still  something 
to  explain  at  this  point. 

It  must  be  noticed,  however,  that  the  difficulties 
here  mentioned  are  not  necessarily  difficulties  for 
evolution,  but  only  for  certain  theories  of  evolution. 
Pure  Darwinism  meets  serious  obstacles  at  these 
points.  The  trouble  is  simply  in  our  understanding 
of.  the  manner  in  which  organs  could  have  become 
rudimentary ;  and  although  we  may  not  yet  compre- 
hend this,  the  presence  of  rudimentary  aborted 
organs  is  just  as  significant  an  argument  for  descent 
as  it  would  be  did  these  difficulties  of  method  not 
exist. 

Nascent  Organs. 

The  second  class  of  rudimentary  organs  are  those 
which  Agassiz  has  been  pleased  to  call  prophetic 
organs,  and  which  evolution  would  call  nascent 
organs.  They  are  organs  which,  very  simple  in  low 


NASCENT  ORGANS.  83 

animals,  seem  there  to  foreshadow  the  coming  of 
homologous  organs,  highly  developed  in  higher 
animals.  As  good  an  example  as  can  be  chosen  of  a 
nascent  organ,  is  the  air-bladder  of  fishes.  It  is  of 
very  little  use  to  the  fish,  or,  at  all  events,  is  only 
valuable  for  a  hydrostatic  apparatus  ;  but  it  occurs  in 
such  relations  as  to  show  that  it  is  the  undoubted 
homologue  of  the  lungs  of  land  animals.  Occurring 
in  low  animals,  while  lungs  only  belong  to  those 
more  highly  developed,  it  cannot  be  regarded  as 
the  aborted  remnant  of  a  previously  functional 
lung,  for  the  ancestors  of  fishes  never  possessed 
lungs.  Agassiz  considered  them  to  be  prophecies  of 
the  coming  lungs;  an  idea  in  perfect  accordance 
with  his  general  theory  of  types  existing  in  the 
Creator's  mind,  but  of  no  meaning  otherwise. 

But  the  theory  of  descent  has  also  its  explanation 
of  these  cases,  which  is  as  intelligible,  and  has  the 
advantage  of  being  natural  rather  than  supernatural. 
These  organs  are  considered  not  as  remnants  but  as 
beginnings.  They  are  new  organs,  capable  of  fur- 
ther development,  and  not  organs  on  their  way 
toward  disappearance.  The  theory  claims,  more- 
over, that  they  are  not  functionless,  like  those  re- 
sulting from  disuse,  but  are  of  some  value  to  their 
possessor,  although  the  value  may  be  a  slight  one. 
Every  organ,  according  to  the  descent  theory,  must 
make  its  appearance  as  a  very  simple  structure, 
which  gradually  develops,  generation  after  genera- 
tion, and  in  the  course  of  time  may  become  very 
greatly  developed.  A  very  simple  organ  in  a  low 
animal  may  therefore  evidently  be  some  such  rudi- 


84  EVOLUTION  OF  TO-DAY. 

mentary  beginning.  To  use  once  more  the  above 
illustration  :  the  descent  theory  would  say  that  the 
air-bladder  of  fishes  is  not  a  useless  organ,  being  of 
importance  as  a  hydrostatic  apparatus,  and  its  pres- 
ence in  the  fish  is  explained,  not  as  a  prophecy  of 
coming  lungs,  but  as  being  of  direct  use  to  the  ani- 
mal. The  theory  would  go  on  to  say,  that  this  air- 
bladder  in  certain  fishes  in  the  past  became  more 
complicated,  and  that  in  some  cases  there  was  de- 
veloped within  its  walls  a  considerable  supply  of 
blood-vessels,  so  that  by  taking  air  into  this  air- 
bladder  the  fish  could  carry  on  a  certain  amount  of 
its  respiration.  And  this  is  not  hypothesis  simply, 
for  some  fishes  (Dipnoi)  do  make  use  of  swallowed 
air  in  this  way.  Now  these  fishes,  the  theory  goes 
on  to  say,  being  able  to  respire  slightly  by  means  of 
this  highly  developed  air-bladder,  would  be  able  to 
survive  if  left  upon  the  beach  for  a  short  time  by 
the  retreating  tide.  Perhaps  they  would  acquire  the 
habit  of  escaping  from  their  enemies  by  retreating 
into  shallow  water  when  the  fall  of  the  tide  would 
leave  them  for  some  time  exposed  to  the  air.  Such 
favored  individuals  would  survive  and  multiply,  and 
the  habit  of  breathing  air  would  become  more 
marked.  Finally,  the  air-bladder  would  become  so 
well  developed  by  use,  that  its  possessor  could  live 
for  a  long  time  out  of  water,  breathing  air  by  its 
means,  or  could  still  live  in  the  water  like  a  fish  :  a 
condition  found  in  the  amphibia.  A  true  land  ani- 
mal would  thus  arise  breathing  by  means  of  lungs. 
Meantime  other  fishes  whose  air-bladders  did  not 
present  these  favorable  variations,  or  who  did  not 


NASCENT  ORGANS.  8$ 

make  use  of  them,  would  still  retain  this  organ  as  a 
hydrostatic  apparatus.  And  thus  we  find  the  air- 
bladder  to-day  the  homologue  of  the  lung,  but  not 
a  remnant  of  a  formerly  functional  lung,  nor  a 
prophecy  of  a  future  lung,  but  a  rudimentary  be- 
ginning, which  is  or  has  been  capable  of  further 
development.  It  is  not,  of  course,  claimed  that  such 
has  been  the  exact  history  of  the  development  of 
the  lung,  for  of  exact  history  we  are  profoundly 
ignorant.  The  example  has  been  taken  as  an  illus- 
tration of  the  sort  of  explanation  which  the  evolu- 
tion theory  has  to  offer  for  nascent  rudimentary 
organs.  It  was  the  presence  of  this  highly  variable 
air-bladder  which  enabled  the  early  land  animal  to 
leave  the  water,  for  a  short  time  at  first,  but  after- 
wards for  longer  periods.  The  rudimentary  lung, 
or  vascular  air-bladder,  did  not  appear  in  order  that 
animals  might  become  air-breathers,  but  animals 
became  air-breathers  to  escape  their  enemies,  as 
soon  as  their  air-bladders,  varying  by  chance  or 
otherwise,  enabled  them  to  do  so.  This  air-bladder 
was  the  cause  of  air-breathing,  but  not,  according  to 
the  descent  theory,  created  for  this  distinct  purpose. 
They  were  the  predecessors,  but  not  the  prophecies, 
of  lungs. 

It  is  by  no  means  always  possible  to  determine  of 
a  given  structure  whether  it  be  an  atrophied  rem- 
nant or  a  nascent  organ ;  and  indeed  sometimes  it 
may  partake  partially  of  both  characters.  It  would 
be  expected  that  an  atrophied  organ  would  be  very 
similar  in  form  to  its  developed  homologue,  but 
much  smaller,  and  with  various  parts  lost  or  fused 


86  EVOLUTION  OF  TO-DAY. 

together  ;  while  on  the  other  hand  a  nascent  organ 
would  probably  be  very  different  in  many  respects. 
Again,  an  atrophied  organ  would  always  be  func- 
tionless,  while  a  nascent  organ  would  have  some 
function,  though  frequently  a  different  one  from 
that  possessed  by  its  developed  homologue.  Thus 
it  is  easy  to  decide  that  the  rudimentary  leg  of  the 
snake  is  an  atrophied  organ,  while  the  fin  of  a  fish  is 
probably  to  be  considered  as  a  nascent  structure. 
But  although  it  may  not  always  be  possible  to  dis- 
tinguish into  which  category  to  place  a  given  organ, 
it  must  be  recognized  that  the  theory  of  descent  as 
well  as  the  theory  of  types  comprehends  and  ex- 
plains both. 

Summary. 

A  careful  study  of  living  things  has  been  slowly 
but  persistently  forcing  naturalists  to  the  conclusion 
that  the  organic  world  forms  a  unit.  Species  are 
found  to  graduate  into  each  other,  and  so,  too,  do 
genera  show  connecting  links.  If  we  take  into  cog- 
nizance the  discoveries  of  paleontology,  we  find  that 
the  larger  groups  of  families  and  orders  exhibit  the 
•same  tendency  toward  convergence.  And  when, 
finally,  we  consider  the  evidence  of  embryology,  the 
great  sub-kingdoms,  and  even  the  kingdoms  of  ani- 
mals and  plants,  come  together.  The  whole  organic 
world  is  thus  found  to  be  related  in  groups  sub- 
ordinate to  groups,  a  relation  which  is  diagrammat- 
ically  represented  by  a  highly  branching  tree,  each 
twig  of  which  is  related  either  closely  or  distantly  to 
every  other.  And  that  such  a  conception  of  the  re- 


SUMMARY.  S/ 

lations  of  the  organic  world  represents  the  true  one, 
is  admitted  by  all  who  have  taken  the  trouble  to 
study  into  the  matter. 

Recognizing  that  a  classification  exists,  it  is  neces- 
sary, if  possible,  to  give  some  reason  why  it  should 
exist ;  recognizing  a  unity,  it  is  desirable  to  find 
the  bond  of  union.  In  answer,  only  two  important 
theories  have  been  advanced — the  theory  of  types, 
which  finds  the  bond  of  union  in  the  creating  mind, 
and  the  theory  of  evolution,  which  finds  it  in  the 
principle  of  descent.  The  first,  in  spite  of  the  mas- 
terly attempt  of  Agassiz  to  establish  it,  has  been 
constantly  losing  ground  since  the  appearance  of 
the  second.  The  impossibility  of  deciding  even  as 
to  the  number  of  types,  to  say  nothing  of  the  im- 
possibility of  defining  them  ;  the  infinite  number  of 
sub-types,  and  types  within  types,  required  to  ex- 
plain smaller  groups  ;  the  impossibility  of  finding  a 
position  for  many  animals  under  any  of  the  great 
types ;  the  gradual  approach  of  the  groups  toward 
each  other  in  their  simpler  and  earlier  forms,  and 
if  embryology  be  taken  as  evidence,  the  union  of 
the  sub-kingdoms,  and  kingdoms  with  each  other,  at 
a  common  starting-point;  and  finally  (and  this  has 
in  reality  had  more  weight  than  the  rest),  the  fact 
that  this  explanation  is  a  transcendental  and  not  a 
natural  one  ;— all  of  these  considerations  have  led  to 
the  gradual  abandonment  of  the  theory  of  types. 

But  the  disproof  of  the  first  theory  does  not,  of 
course,  prove  the  second.  Each  must  stand  on  its 
own  merits,  and  not  upon  the  disproof  of  the  other. 
We  do  find,  however,  that  the  evolution  theory  is 


88  EVOLUTION  OF  TO-DAY. 

in  accordance  with  the  evidence.  Upon  examina- 
tion, it  is  found  to  fit  the  facts  marvellously  well,  and 
to  do  away  with  many  perplexing  problems.  With 
careful  study  this  theory  has  been  found  to  offer  a 
simple  explanation  to  many  classes  of  facts  which 
had  hitherto  been  troublesome  puzzles.  The  theory 
has,  it  is  true,  raised  certain  difficulties  of  its  own, 
for  it  has  found  itself  unable  to  explain  every  thing. 
The  problem  of  serial  homology,  and  the  difficulty 
of  understanding  the  degradation  of  organs  to  a 
rudimentary  condition,  and  their  final  disappearance, 
are  the  chief  ones,  but  even  these  are  difficulties  for 
Darwin's  explanation  of  evolution,  and  not  for  the 
descent  theory  itself.  Admitting,  however,  their  full 
force,  they  are  not  sufficient  to  offset  the  great  ad- 
vantages offered  by  the  descent  explanation.  No 
one  thoroughly  acquainted  with  the  organic  world 
hesitates  to  say  that  the  theory  of  descent  must  be 
admitted  as  a  factor,  though  perhaps  not  the  only 
.factor.  As  a  conclusion  from  the  study  of  classifi- 
cation, it  seems  that  we  must  either  accept  evolution 
as  the  explanation  of  the  bond  of  union  in  the 
organic  world,  or  wait  for  some  other  better  theory, 
of  which  the  descent  idea  will  doubtless  form  a 
part. 


CHAPTER  III. 

LIFE   DURING   THE   GEOLOGICAL  AGES. 

THE  fossils  of  the  stratified  rocks  are  believed  to 
give  a  history  more  or  less  complete  of  the  life  of 
the  world  during  past  ages.  Here  it  is,  therefore, 
that  we  should  expect  the  most  complete  evidence 
toward  settling  the  question  of  the  origin  of  species. 
If  existing  organisms  have  been  slowly  evolved  from 
others,  and  if  paleontology  gives  us  a  history  of  the 
past,  we  might  here  expect  something  like  proof. 
The  necessity  of  appealing  to  paleontology  has 
been  seen  by  all  scientists,  and  one  of  Darwin's 
most  difficult  tasks  was  in  endeavoring  to  reconcile 
the  known  facts  of  this  science  with  his  views  of 
evolution.  For  it  is  safe  to  state  that  paleontology 
has  offered  to  Darwin  and  his  followers  greater  dif- 
ficulties than  any  other  branch  of  science.  Here, 
where  it  would  seem  the  strongest  evidence  might  be 
expected,  have  been  found  the  most  serious  obsta- 
cles, and  the  evidence  has  been  the  weakest.  At 
least  this  was  true  at  the  time  of  the  appearance  of 
the  "  Origin  of  Species,"  and  Darwin  with  his  usual 
candor  acknowledged  the  great  difficulties  thus 
arising.  Since  that  time  there  have  been  great  addi- 
tions to  our  collections  and  knowlege  of  fossils,  and 
89 


QO  EVOLUTION  OF  TO-DAY. 

a  great  amount  of  positive  evidence  has  been  accu- 
mulated. But  the  subject  is  still  in  an  unsatisfac- 
tory condition,  and  in  spite  of  all  advance  the  chief 
difficulties  occurring  to  Darwin  and  others  thirty 
years  ago  have  not  been  removed,  but  stand  out  as 
boldly  as  ever.  The  evidence  collected  has,  it  is 
true,  added  very  much  positive  evidence  in  support 
of  the  general  theory,  and  in  many  cases  we  now 
have  practical  proof  of  the  gradual  origin  of  species 
from  each  other.  But  even  yet  there  is  not  the 
slightest  difficulty  for  any  one  so  inclined  to  point 
out  many  places  where  paleontology  disagrees  with 
the  deductions  of  evolution,  for  the  past  history  of 
the  world  as  taught  by  its  fossils  still  offers  many 
difficulties  to  the  descent  theory. 

Imperfection  of  the  Record. 

It  has  been  clearly  recognized  by  all  scientists, 
that  it  is  absolutely  impossible  to  reconcile  paleon- 
tology with  evolution,  unless  it  be  assumed,  to  start 
with,  that  the  history  of  animals  which  we  get  from 
fossils  is  extremely  imperfect.  According  to  evolu- 
tion, our  present  species  are  descended  from  others, 
quite  different  from  them,  living  in  the  past.  Not 
long  ago,  the  various  species  of  our  now  existing 
genera  were  simply  varieties  of  an  ancestral  spe- 
cies. Still  earlier,  the  genera  of  our  present  families 
were  in  turn  only  varieties  of  a  still  older  ancestral 
species.  The  present  orders  and  classes  also  ought 
gradually  to  converge  toward  some  very  ancient 
generalized  ancestor.  All  of  this  history  has  been  a 
continual  slow  growth,  according  to  the  ordinary  con- 


IMPERFECTION   OF  THE  RECORD.  9! 

ception  of  evolution.  There  have,  therefore,  existed 
between  the  animals  of  to-day  and  their  ancient  an- 
cestors  a  long  series  of  intermediate  links.  In  each 
case  these  connecting  individuals  will  differ  from  their 
parents  no  more  than  the  child  differs  from  its  parents 
to-day.  But  the  number  has  been  so  great  that  the 
slight  differences  accumulated  through  the  ages 
have  finally  amounted  to  wide  distinctions.  If  fos- 
sil history  gives  us  any  thing  like  a  complete  record 
of  the  past,  all  of  these  stages,  or  at  least  many  of 
them,  ought  to  be  found.  By  means  of  fossil  links, 
therefore,  all  generic  and  specific  differences  should 
disappear  in  a  graduated  series  of  connective  links. 
But  no  one  ever  pretended  to  claim  that  any  such 
a  series  could  be  found.  Paleontology  at  the  time 
of  the  appearance  of  Darwirf's  book  showed  very 
few  such  connecting  links  ;  while  to-day  many  more 
are  known,  they  are  really  as  nothing  compared 
with  the  countless  numbers  which  must  have  ex- 
existed.  We  know  enough  of  fossils  to-day  to 
cause  us  to  abandon  hope  of  ever  making  out  such 
a  complete  history  as  the  theory  calls  for.  Perceiv- 
ing the  great  lack  of  these  intermediate  stages,  some 
naturalists  have  been  led  to  modify  the  first  concep- 
tion of  evolution.  Many  hold  the  position  to-day, 
that  development  in  the  past  has  not  always  been 
slow  and  gradual,  but  by  alternate  periods  of  rapid 
development  and  comparative  rest.  This  saltatory 
evolution,  as  it  is  called,  does  not  demand  such  a 
long  series  of  intermediate  links.  It  assumes  that 
under  certain  unknown  circumstances  species  are 
very  rapidly  modified,  and  that  a  few  generations 


92  EVOLUTION  OF  TO-DA  Y. 

only  are  required  to  produce  much  change.  If  this 
were  true  we  would  only  expect  to  find  evidence  of 
the  periods  of  rest,  the  periods  of  change  being  too 
brief  to  give  much  chance  for  preservation.  While, 
then,  fossils  do  not  show  the  numerous  stages  of  a 
slow  evolution,  it  is  possible  that  the  fossil  record 
may  be  in  harmony  with  this  saltatory  evolution. 

But  even  with  this  modified  and  more  favorable 
form  of  evolution  in  mind,  the  record  of  paleon- 
tology cannot  be  regarded  otherwise  than  as  re- 
markably imperfect.  Its  imperfection  is  indeed  a 
necessity  for  evolution.  Nor  can  there  be  the 
slightest  doubt  as  to  the  teaching  of  recent  years 
on  this  matter.  All  evidence  from  every  source 
emphasizes  the  fact  that  the  paleontological  record 
is  very  imperfect ;  that  the  few  animals  which  we 
have  preserved  are  almost  as  nothing  compared 
with  the  countless  myriads  which  have  disappeared 
and  left  no  trace.  Indeed  recent  years  would  indi- 
cate that  this  imperfection  is  even  greater  than 
assumed  by  Darwin.  The  discovery,  in  quite  a 
number  of  cases,  of  a  single  imperfect  specimen 
of  an  animal  in  a  bed  of  rocks  whose  accumulation 
must  have  taken  thousands  of  years,  is  a  slight  indi- 
cation of  what  we  may  look  for  in  this  direction. 
The  causes  of  this  imperfection  are  very  varied. 
The  chief  are  as  follows:  (i)  Only  those  animals 
which  possess  some  sort  of  hard  skeleton  can  be 
preserved  as  fossils,  soft  animals  leaving  almost  no 
impression  in  the  sedimentary  rocks.  This  is 
demonstrated  by  the  fact  that  about  nine  tenths  of 
the  orders  which  are  entirely  unrepresented  in  the 


IMPERFECTION  OF  THE  RECORD,  93 

rocks  have  no  skeleton.  This  is  the  more  important, 
because  in  very  many  cases  the  animals  which  we 
must  look  for  as  ancestral  types,  could  have  pos- 
sessed no  skeleton.  For  instance,  the  original 
vertebrate  ancestor  could  not  have  had  a  skeleton, 
and  we  can  therefore  have  no  hopes  of  finding  any 
record  of  its  existence  among  fossils.  (2)  Fossils 
can  only  be  deposited  during  the  accumulation  of 
sediment,  and,  therefore,  during  periods  of  slow 
subsidence  at  the  localities  in  question.  All  periods 
of  elevation,  or  of  rapid  subsidence,  will  be  almost 
or  entirely  unrepresented  in  the  geological  record. 
How  great  these  gaps  may  be,  we  have  no  means 
of  determining,  but  they  are  doubtless  enormous. 
(3)  Fresh-water  and  land  animals  can  only  be  pre- 
served by  being  carried  to  the  sea,  or  some  inland 
lake  which  is  filling  up ;  or  by  being  deposited  in 
the  river  beds.  Evidence  of  this  is  found  in  the 
great  scarcity  of  fresh -water  fossils,  and  particularly 
in  the  remarkable  scarcity  of  insects  in  all  rocks — a 
group  which  must  have  existed  in  numbers,  but 
whose  light  bodies  prevent  them  from  sinking  to 
the  bottom  of  the  water.  (4)  Many  of  the  rocks, 
particularly  those  of  the  earlier  ages,  have  been 
subjected  to  such  great  metamorphic  changes,  that 
whatever  fossils  they  might  once  have  contained 
have  been  entirely  or  partially  destroyed.  These 
four  factors,  with  other  minor  ones,  have  appeared 
sufficient  to  geologists  to  justify  the  belief  in  almost 
any  amount  of  imperfection  in  the  geological  record. 
This  imperfection  is  certainly  growing  less  with 
the  continual  study  of  new  localities,  for  many  gaps 


94  EVOLUTION  OF  TO-DAY. 

are  being  thus  filled.  One  striking  evidence  of  this 
is  in  the  gradual  disappearance  of  the  lines  of 
demarkation  between  the  different  geological  ages. 
Geologists  no  longer  recognize  the  history  of  the 
world  as  divided  into  distinct  ages,  but  look  upon 
it  as  continual  progression.  The  lines  of  demarka- 
tion between  the  formerly  accepted  ages  are  due  to 
the  almost  universal  gaps  in  the  record  at  certain 
periods — gaps  which  are  slowly  being  filled  by  new 
discoveries. 

Having  reached  this  conception  of  the  imperfec- 
tion of  the  record,  the  evolutionist  seems  to  have 
assumed  an  unassailable  position.  For  whatever 
connecting  links  chance  to  be  found,  they  are 
immediately  claimed  as  positive  arguments,  while 
the  difficulties  arising  from  absence  of  links  are 
readily  answered  by  appeal  to  the  imperfection  of 
the  record.  It  is  not  easy,  therefore,  to  discuss  the 
subject  except  by  beginning  with  the  begging  of  the 
question. 

The  First  Appearance  of  Life. 

The  chief  difficulties  offered  by  this  branch  of 
science  to  the  theory  of  evolution,  cluster  around 
the  life  of  the  Silurian  age,  the  earliest  age  in 
which  fossils  appear.  The  still  earlier  archean  rocks 
do  contain  the  well-known  Eozoan  Canadense, 
which  is  supposed  by  some  to  be  a  fossil.  But  it  is 
very  questionable  whether  this  deposit  is  any  thing 
more  than  a  mineral.  It  is  found  in  the  oldest 
rocks,  which  contain  no  other  traces  whatsoever  of 
any  other  organic  remains.  Dawson,  its  discoverer, 


THE  FIRST  APPEARANCE   OF  LIFE.  95 

believes  it  to  be  a  low  foraminiferon  ;  but  later 
researches  make  this  very  doubtful.  The  direct 
examination  of  the  deposit  itself  scarcely  lends 
support  to  the  belief  in  its  organic  nature.  It  is 
found  in  the  lower  Laurentian  rocks,  which  are  cov- 
ered with  thousands  of  feet  of  rocks  less  metamor- 
phosed than  those  containing  the  Eozoan,  and  yet 
themselves  containing  no  fossils.  It  now  appears, 
also,  that  this  so-called  fossil  is  sometimes  found  in 
veins  in  the  rocks,  and  this  position  is  utterly 
impossible  for  a  true  fossil.  These  facts,  therefore, 
render  it  improbable  that  the  Eozoan  is  any  thing 
more  than  a  mineral  deposit ;  and  lead  to  the  con- 
clusion that  the  first  traces  we  have  of  life  begin 
with  the  Silurian  age.  But  whether  it  be  a  true 
animal  or  not,  does  not  materially  affect  the  difficul- 
ties surrounding  the  sudden  appearance  of  a  highly 
differentiated  fauna  in  the  very  beginning  of  the 
Silurian  age.  The  first  record  we  have  of  life  is 
very  surprising.  Instead  of  a  few  low  forms  of  life, 
instead  of  a  few  synthetic  genera,  the  Silurian  age 
was  supplied  with  a  highly  developed  fauna  of 
comparatively  highly  organized  animals.  All  of 
the  great  types  were  represented :  Coelenterata, 
Polyzoa,  Brachiopods,  Echinoderms,  Mollusks, 
Worms,  Arthropoda ;  and  the  late  discoveries  of 
Claypole  have  traced  the  vertebrates  not  indeed  to 
the  bottom  of  the  Silurian,  but  to  the  bottom  of 
the  upper  Silurian  rocks,  a  number  of  remains 
proving  that  fishes  were  then  in  existence.  Within 
a  few  months  two  scorpions  have  been  added  to  the 
Silurian  fauna,  adding  another  class  to  the  already 


96  EVOLUTION  OF  TO-DAY. 

extensive  list.  It  is  true  that  not  all  of  these 
animals  are  found  at  the  very  bottom  of  the  Silu- 
rian, but  even  in  the  oldest  rocks  the  fauna  is  suffi- 
ciently diverse  ;  and  before  the  age  is  over,  all  of 
the  important  classes  of  animals  have  made  their 
appearance  without  previous  warning.  This  sudden 
appearance  of  life  is  certainly  unexpected.  The 
possible  organic  nature  of  the  Eozoan  in  the  older 
rocks  is  no  help  toward  solving  the  difficulty. 
Should  this  prove  to  be  a  fossil,  it  only  shows  that  it 
was  possible  for  fossils  to  be  preserved  during  the 
pre-Silurian  times.  Evolution  must,  of  course, 
suppose  that  it  was  during  this  period  that  the  first 
forms  of  life  were  developing  into  the  condition 
which  we  find  with  the  beginning  of  the  Silurian. 
The  question  is  even  more  forcibly  asked,  if  the 
Eozoan  be  a  fossil,  why  we  find  no  trace  of  this 
early  fauna  ? 

The  only  possible  explanation  of  this  sudden  ap- 
pearance of  life  in  the  Silurian,  is  an  appeal  to  the 
incompleteness  of  the  record.  Vast  periods  of  time 
must  have  elapsed  before  the  Silurian  times,  during 
which  the  world  was  peopled  with  living  things, 
every  trace  of  which  must  be  supposed  to  have  been 
lost.  There  can  be  no  doubt  that  there  was  an 
enormous  period  of  time  between  the  solidifying  of 
the  world  and  the  beginning  of  the  Silurian.  But 
whether  the  world  was  inhabited  at  this  time  it  is 
impossible  to  prove.  That  a  long  period  elapsed 
between  the  latest  pre-Silurian  rocks  of  any  one 
locality  and  the  earliest  Silurian,  is  also  unques- 
tioned. But  how  long  this  lost  period  might  have 


THE  FIRST  APPEARANCE   OF  LIFE.  97 

been,  is  simply  a  matter  of  conjecture.  The  two 
periods  together  must  have  been  long  enough  to 
account  for  the  development  of  the  Silurian  fauna 
out  of  the  simplest  form  of  animal,  or  the  evolution 
theory  falls  to  the  ground.  Whether  this  appeal  to 
these  enormous  lost  intervals  is  considered  sufficient 
to  explain  the  sudden  appearance  of  life  in  the 
Silurian  age,  will  depend  largely  upon  one's  previous 
views  as  to  the  significance  of  the  whole  question  of 
evolution.  If  we  wish  to  accept  evolution,  we  can 
readily  believe  this  explanation  to  be  satisfactory; 
if  we  do  not  wish  to  do  so,  we  can  find  here  an 
almost  insurmountable  difficulty. 

This  same  difficulty  of  time  has  been  attacked 
from  another  standpoint,  by  an  attempt  to  reduce 
to  years  some  of  the  intervals.  Darwin  has  set  as 
the  lowest  limit  which  he  considers  necessary  for 
the  development  of  the  now  existing  species,  three 
hundred  millions  of  years.  Mivart,  ostensibly  tak- 
ing the  facts  given  him  by  Darwin,  considers  that 
twenty-five  hundred  millions  of  years  is  nearer  the 
limit.  This  estimate  is,  however,  worthless,  as  the 
very  data  upon  which  it  is  founded  are  simple 
guesses.  On  the  other  hand,  Sir  Wm.  Thomson  has 
concluded  from  cosmic  phenomena,  that  the  solidi- 
fication of  the  earth  took  place  probably  not  more 
than  one  hundred  millions  of  years  ago.  Dr.  Croll 
considers  this  conclusion  almost  indisputable.  The 
age  of  the  inhabitable  world  is  thus  much  less  than 
the  necessities  of  Darwinism  demand. 

These  estimates  can  only  be  reconciled  by  short- 
ening the  time  required  for  the  development  of 


98  EVOLUTION  OF  TO-DAY. 

species.  The  estimates  of  the  age  of  the  world, 
made  from  geological  researches  of  late  years,  are 
smaller  than  those  of  twenty  years  ago,  and  fall 
readily  within  the  estimate  of  Sir  Wm.  Thomson. 
The  only  difficulty  lies  in  Darwin's  three  hundred 
millions  of  years.  Now  this  estimate  of  Darwin  is 
nothing  more  than  a  guess.  We  know  almost 
nothing  concerning  the  rate  of  modification  of 
species  to-day,  not  to  speak  of  our  absolute  ignor- 
ance of  what  it  may  have  been  in  the  past.  Sir 
Wm.  Thomson  insists  that  the  physical  changes 
were  more  rapid  in  early  times  than  they  are  now, 
and  this  would  necessitate  a  proportionate  rapidity 
in  the  changes  of  the  organic  world.  Moreover, 
modern  embryology,  as  we  shall  see .  in  the  next 
chapter,  seems  to  indicate  that  the  history  of 
animals  has  not  been  so  long  and  circuitous  as  was 
once  supposed.  Instead  of  passing  through  a  long 
series  of  great  changes,  all  of  the  large  groups  of 
animals,  even  the  vertebrates,  have  had  a  direct  sim- 
ple history  from  the  simplest  multicellular  animal. 
This  early  ancestral  animal  branched  off  directly 
into  several  directions,  and  thus  the  time  necessary 
for  the  development  of  a  diverse  fauna  like  that  of 
the  Silurian  age  is  less  than  could  formerly  be  sup- 
posed. Again,  the  time  since  the  Silurian  age  has 
been  sufficient  to  develop  the  group  of  vertebrates 
from  its  simplest  form  to  its  present  condition,  and 
an  equal  amount  of  time,  and  probably  a  much 
shorter  period,  before  the  Silurian  age,  would  be 
amply  sufficient  to  account  for  the  primordial 
fauna.  The  duration  of  this  period  in  years  is  of 


ABSENCE   OF  GENERALIZED  FORMS,  99 

little  importance  to  our  subject,  the  amount  of 
geological  change  being  the  important  factor;  for 
rapid  geological  changes  will  cause  rapid  organic 
developments.  If,  then,  it  is  true,  as  embryology 
teaches,  that  the  first  variations  from  the  original 
ancestral  type  produced  directly  the  various  sub- 
kingdoms  of  animals,  and  if,  further,  the  changes 
were  more  rapid  at  this  early  period,  it  becomes 
probable  that  the  time  required  for  the  establish- 
ment of  the  types  of  the  Silurian  period,  was  not  so 
long  as  would  be  required  for  what  would  seem  to 
be  an  equal  amount  of  change  in  animals  as  they 
exist  to-day. 

The  A  bsence  of  Generalized  Forms  from  the  Silurian. 

This  old  Silurian  fauna  is  puzzling  in  another  re- 
spect. It  is  undoubtedly  a  highly  specialized  fauna. 
It  has  been  and  is  still  forcibly  urged  that,  accord- 
ing to  evolution,  the  farther  back  we  go,  the  greater 
and  greater  should  be  the  generic  likeness  of  fos- 
sils, and  the  less  and  less  their  specialization.  For 
if  our  classes,  orders,  and  genera  existed  at  any  time 
as  simple  species,  the  fossils  ought  all  to  be  more 
or  less  generalized  forms  ;  i.  e.,  forms  possessing  the 
fundamental  characters  of  all  the  classes  that  arise 
from  them.  The  oldest  fossils  ought  to  be  almost 
entirely  of  this  character.  The  number  of  species 
should  become  less  and  less,  and  it  might  be  ex- 
pected that  in  the  earlier  ages  we  should  find  almost 
nothing  corresponding  to  species,  since  no  speciali- 
zation would  have  taken  place.  But  it  is  further 
pointed  out  that  this  is  not  the  teaching  of  paleon- 


IOO  EVOLUTION  OF  TO-DAY. 

tology.  At  the  beginning  of  our  record  of  life,  the 
world  was  not  filled  with  a  few  generalized  types, 
but  with  an  already  well-differentiated  fauna  of 
genera  and  species.  For  instance  :  the  Echinoderms, 
instead  of  consisting  of  a  few  generalized  types,  were 
already  divided  into  the  perfectly  distinct  orders, 
Crinoids,  Blastids,  Cystids,  Asteroids,  Ophiuroids, 
and  Echnoids.  All  had  their  special  genera  and 
species,  and  almost  none  of  them  such  as  can  be 
imagined  to  have  given  rise  to  the  groups  of  later 
times. 

This  claim  is,  however,  partially  a  misunderstand- 
ing, for  it  seems  to  imply  that  we  should  expect  to 
find  animals  which  were  purely  generalized,  with  no 
specific  characters.  The  most  comprehensive  types 
which  ever  existed  must  have  had,  along  with  their 
general  characteristics,  their  own  special  features, 
which  adapted  them  to  surroundings.  While  they 
would  be  synthetic  in  that  they  shared  the  char- 
acters of  many  different  forms,  each  one  would 
also  be  distinctly  specialized.  No  animal  could  ex- 
ist without  having  definite  shape,  size,  color,  etc., 
and  these  characters  would  be  specific.  It  is,  then, 
not  at  all  surprising  that  we  find  even  in  the  Silurian 
a  specialized  fauna  and  flora,  for  it  could  not  have 
been  otherwise.  And,  moreover,  it  is  perfectly  in- 
telligible that  some  of  the  simple  groups,  even  at 
that  early  date,  could  have  become  highly  special- 
ized, as  highly,  in  fact,  as  they  became  afterwards. 
The  force  of  the  difficulty  here,  as  far  as  it  is  a  diffi- 
culty, lies  not  in  the  presence  of  specific  distinctions, 
but  in  the  absence  of  generalized  characteristics. 


ABSENCE   OF  GENERALIZED  FORMS.  IOI 

It  must  not  be  understood,  however,  that  no  syn- 
thetic types  have  been  found  at  this  early  period, 
for  many  are  well  known ;  but  it  is  a  fact  that  their 
number  is  very  few  compared  with  the  highly 
specialized  types  which  possessed  no  synthetic  fea- 
tures. Upon  the  theory  of  evolution,  great  numbers 
of  these  synthetic  types  must  have  then  existed, 
and  it  can  be  well  asked  why  we  get  no  more  traces 
of  them.  It  is  a  significant  question  to  ask  where 
are  any  traces  of  the  simple  generalized  vertebrate 
which  must  have  lived  in  the  Silurian  age,  possess- 
ing the  characteristics  of  all  classes  of  vertebrates. 
But  at  the  same  time  we  can  readily  understand 
how  other  groups  of  simple  animals  should  have 
met  with  such  favorable  conditions  as  to  give  rise 
to  rapid  divergence  and  specific  distinction.  The 
high  specialization  present  in  some  of  the  Silurian 
fauna,  the  great  numbers  of  highly  developed  forms 
of  Brachiopods,  Echinoderms,  Crustacea,  etc.;  the 
great  profusion  of  reptiles  in  the  Jurassic,  the  abun- 
dance of  plants  in  the  Dakota  group,  require  no 
special  explanation.  But  the  absence  of  cotempo- 
raneous  forms,  with  generalized  characteristics,  is  for 
evolution  unfortunate. 

Two  reasons  for  this  can  be  given.  Firstly,  there 
are  certain  definite  reasons  for  believing  that  at 
these  very  points  the  imperfection  of  the  record 
would  be  great.  As  a  rule,  the  generalized  forms 
which  we  would  expect,  would  be  those  which  from 
absence  of  hard  parts  could  not  be  preserved.  The 
primitive  vertebrate,  for  instance,  could  have  pos- 
sessed no  skeleton, — at  least  nothing  more  than  a 


IO2  EVOLUTION  OF  TO-DAY. 

gelatinous  rod  for  a  back-bone, — and  this  could  not 
have  been  preserved  as  a  fossil.  If  this  animal  pos- 
sessed scales,  the  scales  might  have  been  preserved ; 
and  we  do  find  certain  fish-scales  at  this  period. 
But  simple  scales  of  course  give  us  no  idea  as  to 
what  sort  of  an  animal  possessed  them.  For  all  that 
we  know  this  animal  may  have  been  exactly  the  syn- 
thetic type  we  are  looking  for.  And  so  in  many 
cases,  the  early  ancestral  forms  of  various  groups 
must  have  been  animals  with  very  few  hard  parts, 
and  there  would  be,  therefore,  no  chance  of  their 
preservation. 

A  second  reason  for  the  abundance  of  specialized 
forms  compared  with  the  synthetic  types  is,  that 
they  doubtless  existed  in  greater  numbers.  Nor  is 
this  begging  the  question,  as  it  at  first  sight  seems  to 
do.  A  synthetic  type  can  only  remain  synthetic  by 
existing  in  small  numbers.  All  experience  teaches 
us  that  as  soon  as  any  animal  begins  to  multiply 
rapidly  it  becomes  rapidly  specialized.  It  is  only 
specialized  forms  which  can  exist  in  great  num- 
bers. As  a  result,  we  should  expect  to  find,  at  all 
ages,  that  those  forms  which  become  specialized  to 
adapt  themselves  to  peculiar  conditions,  would  mul- 
tiply the  most  rapidly  and  exist  in  the  greatest  num- 
bers. Here,  then,  is  a  reason  for  the  comparative 
scarcity  of  forms  with  generalized  characteristics,  at 
all  geological  ages, — a  reason  which  would  be  as  sig- 
nificant in  early  times  as  at  present.  A  synthetic 
type  can  remain  synthetic  only  as  long  as  it  exists 
in  small  numbers. 


DIVERSITY  OF  SILURIAN  LIFE.  1 03 

The  Diversity  of  Silurian  Life. 

Still  another  difficulty  has  arisen  in  connection 
with  Silurian  fauna,  closely  related  to  the  one  just 
mentioned.  Our  paleontologists  have  within  the 
last  thirty  years  had  most  wonderful  success  in 
tracing  existing  types  back  to  the  oldest  rocks;  a 
result  which  the  theory  of  descent,  with  modifica- 
tion, would  not  lead  us  to  expect.  It  must  be  ad- 
mitted that  upon  this  theory  we  should  expect  to 
find  the  Silurian  fauna  radically  different  from  that 
existing  now.  Taking  into  account  the  enormous 
time  that  has  elapsed  since  then,  it  would  seem  that 
the  whole  organic  world  would  have  become  altered. 
The  amount  of  modification  possible  in  this  time  is 
shown  by  the  fact  that  the  entire  group  of  verte- 
brates has  developed  into  its  present  condition 
since  the  Silurian.  It  will  probably  be  admitted 
by  every  one  that,  did  we  not  have  any  actual  knowl- 
edge of  the  Silurian,  a  hypothetical  fauna  would 
be  assumed  differing  entirely  from  that  of  to-day. 
It  might  be  admitted  that  there  were  even  then 
specialized  groups  ;  but  it  would  be  supposed  that 
they  had  long  since  passed  away.  Perhaps  a  few 
lingering  forms  might  be  thought  to  have  survived, 
but  in  general  the  old  species,  genera,  orders,  and 
classes  would  have  become  replaced  by  others.  In 
short,  just  such  a  fauna  would  be  assumed  as  is 
now  thought  to  belong  to  the  pre-Silurian  times. 

It  is  true  that  the  fauna  of  to-day  is  different 
from  that  of  the  Silurian  age,  but  the  difference  lies 
chiefly  in  the  species  and  genera.  We  find  that  in  the 
Silurian  fauna  are  represented  all  of  the  sub-king- 


104  EVOLUTION  OF  TO-DAY. 

doms  which  now  exist.  If  now  we  leave  out  of 
account  those  forms  which,  having  no  hard  parts, 
could  not  have  been  preserved,  such  as  worms,  etc., 
we  find  a  large  majority  of  the  groups  have  been 
preserved.  About  five  sixths  of  the  orders,  nearly 
an  equal  proportion  of  sub-orders,  a  great  many 
families,  some  genera,  and  it  has  been  claimed  that 
some  of  our  present  species,  are  known  to  have 
been  in  existence  during  the  Silurian  age.  It  is 
truly  remarkable  to  find  such  a  very  large  portion 
of  existing  groups  represented  in  the  earliest  fauna 
of  which  we  have  any  knowledge.  When  we  re- 
member the  great  imperfection  of  our  knowledge  of 
these  early  animals,  the  difficulty  here  arising  be- 
comes somewhat  formidable.  Still  more  forcible 
does  this  difficulty  become  as  we  realize  that  the 
diversity  of  this  early  life  is  increasing  as  the  record 
is  more  carefully  studied.  The  tendency  of  the  late 
years  of  paleontology  seems  to  indicate  that  if  our 
record  were  more  perfect,  it  would  be  found  that 
nearly  all  our  existing  forms,  down  to  groups  as 
small  as  families,  were  represented  in  the  Silurian 
age.  The  vertebrates  have,  however,  nearly  all  de- 
veloped since  that  time.  And  when  we  compare 
the  great  advance  of  this  sub-kingdom  with  the 
small  advance  of  all  others,  the  contrast  is  very 
striking.  Such  a  result  is  certainly  one  which  evo- 
lution would  not  lead  us  to  expect. 

It  must  be  noticed,  however,  that  this  concession 
to  the  Silurian  fauna  is  too  great,  since  this  age 
lasted  a  very  long  time,  and  many  of  these  modern 
families  did  not  appear  till  toward  its  close.  Bv  the 


DIVERSITY  OF  SILURIAN  LIFE.  IO5 

time  the  Silurian  age  came  to  an  end,  nearly  all 
of  our  existing  families  of  animals  were  probably 
present ;  but  at  the  beginning  they  were  by  no 
means  so  abundant.  But  the  fauna  of  the  very 
earliest  primordial  rocks  was  sufficiently  diversified 
to  be  surprising ;  and  even  with  this  understanding 
of  the  great  length  of  the  Silurian  age,  the  difficulty 
is  still  very  great. 

In  explanation,  one  of  two  assumptions  is  neces- 
sary: either  that  the  time  preceding  the  Silurian 
age  was  much  greater  than  the  time  since  then  — 
and  this  is  highly  improbable  ;  or  that  slight  modifi- 
cations at  the  bottom  of  a  diverging  series  produce 
greater  results  than  equal  modifications  higher  up. 
Starting  with  a  very  simple  ancestral  form  at  the 
bottom  of  the  tree,  it  is  evident  that  slight  varia- 
tions will  immediately  produce  widely  different 
forms,  giving  rise  at  once  to  the  great  branches 
of  the  animal  kingdom  ;  but  after  somewhat  highly 
specialized  forms  have  arisen,  slight  variations  will 
have  less  effect ;  just  as  slight  variations  in  the  direc- 
tion of  the  growing  buds  in  a  very  young  tree  may 
produce  eventually  great  branches,  while  similar 
variations  at  the  ends  of  these  branches,  after  they 
are  grown,  produce  only  twigs.  After  groups  be- 
come highly  specialized,  the  tendency  is  to  produce 
leaves  rather  than  branches  in  zoological  classifica- 
tion. If  this  tendency  express  a  fact,  we  can  per- 
haps get  a  hint  toward  the  elucidation  of  the  above 
difficulties.  Preceding  the  Silurian  age,  enough 
time  must  have  elapsed  since  the  world  was  inhab- 
ited to  produce  the  large  branches  of  the  animal 


IO6  EVOLUTION  OF  TO-DAY. 

kingdom,  and  many  of  the  smaller  ones.  The  in- 
vertebrates in  general,  owing  to  their  comparatively 
simple  organization,  had  already  reached  a  condition 
where  slight  variations  produce  only  twigs,  and  the 
development  has  since  then  been  much  slower. 
The  vertebrates,  however,  developed  more  slowly, 
and  did  not  reach  a  similar  condition  until  much 
later.  The  evidence  indicates,  in  short,  that  the 
power  of  divergence  of  any  type  is  not  unlimited. 
Each  has  a  certain  place  to  fill  in  nature,  and  hav- 
ing once  approximately  filled  it,  the  future  develop- 
ment is  of  such  a  sort  as  to  produce  twigs  rather 
than  branches ;  and  further,  the  evidence  shows  that 
by  the  close  of  the  Silurian,  many  of  the  inverte- 
brate divisions  had  reached  such  a  condition,  while 
the  vertebrates  have  passed  through  nearly  all  of 
their  development  since  that  time.  To  this  latter 
group,  therefore,  must  we  look  for  the  bulk  of  our 
evidence  for  evolution. 

In  this  connection  it  has  frequently  been  urged 
that  the  existence  of  any  animal  unmodified  since 
the  early  Silurian  times,  is  a  grave  difficulty  for  evo- 
lution. The  existence  of  Lingula  (a  small  bivalve 
shell)  with  almost  no  change  since  the  earliest  fossil- 
iferous  rocks,  has  been  regarded  as  a  serious  obstacle 
for  Darwin.  But  this  idea  comes  from  a  misunder- 
standing. Time  does  not  necessarily  imply  change, 
even  upon  the  theory  of  evolution.  Those  organ- 
isms become  modified  which  are  not  in  harmony 
with  their  conditions,  and  consequently  it  requires 
change  of  condition  to  produce  change  of  organic 
structure.  Now  Lingula  is  a  very  simple  animal, 


DISCOVERIES  OF  CONNECTING  LINKS.        IO? 

with  few  enemies  and  a  remarkable  tenacity  of  life. 
It  finds  its  most  congenial  home  on  sand-flats,  and 
these  conditions  must  always  have  existed.  It  is  not 
difficult,  therefore,  to  understand  that,  perfectly 
adapted  to  these  conditions,  with  few  enemies  and 
with  great  tenacity  of  life  enabling  it  to  endure 
considerable  changes,  it  has  continued  to  exist  till 
the  present  day  with  very  slight  modification.  It 
is  suggestive  to  notice  that  another  animal  which 
exhibits  a  similar  tenacity  of  life  is  the  king- 
crab,  also  an  animal  of  very  great  antiquity.  And 
when  with  these  considerations  we  remember  that 
all  of  the  Silurian  animals  which  have  been  pre- 
served were  marine  animals,  and  hence  living  under 
conditions  which  have  remained  practically  the 
same,  we  see  another  suggestion  as  to  the  reason 
why  this  ancient  fauna  has  continued  to  exist  with 
so  little  change. 

Recent  Discoveries  of  Connecting  Links. 

Thus  far  our  attention  has  been  confined  ex- 
clusively to  the  difficulties  offered  to  an  unhesi- 
tating acceptance  of  evolution,  and  it  must  be 
admitted  that  they  are  very  great.  Most  of  them 
were  realized  by  Darwin,  and  he  attempted  to  cope 
with  them.  And  these  difficulties  have  not  grown 
less  since  the  appearance  of  the  "  Origin  of  Species," 
but  have  in  some  respects  grown  greater.  To  ex- 
plain, the  Silurian  fauna,  is  the  greatest  problem 
which  the  evolutionist  has  to  solve  ;  and  except  as  it 
has  emphasized  the  imperfection  of  the  record, 
modern  paleontology  has  not  helped  toward  the 


IO8  EVOLUTION  OF  TO-DAY. 

solution,  but  has  rather  increased  the  difficulty  by 
increasing  the  extent  of  that  ancient  fauna,  and 
making  it  more  like  that  existing  to-day.  Various 
suggestions  have  been  offered  in  explanation  as  de- 
tailed above,  which  show  that  the  problem  is  not 
beyond  solution,  though  they  are  hardly  sufficient 
to  answer  the  objections.  In  spite  of  all,  the  Silurian 
fauna  is  a  surprise,  and  remains  an  unsolved  problem. 

Turning  now  from  these  difficulties  to  positive  evi- 
dence, we  next  ask  whether  the  recent  discoverers 
have  been  successful  in  finding  any  of  the  infinite 
number  of  connecting  links  which  the  theory  as- 
sumes must  have  existed.  And  here  we  find  that 
paleontologists  have  been  successful  almost  beyond 
what  could  have  been  expected.  Naturally  it  is 
the  vertebrates  which  have  furnished  most  of  the 
evidence.  They  form  a  group  which  has  been  de- 
veloped since  the  Silurian  age,  and  are,  moreover, 
well  adapted  for  preservation  as  fossils.  Their  bones 
are  found  in  abundance  in  the  later  formations,  and 
consequently  are  not  metamorphosed.  They  are 
better  known  and  more  studied  than  any  other 
group,  and  it  is  not  surprising,  therefore,  that  most 
of  our  advance  in  paleontology  has  been  in  regard 
to  the  vertebrates.  The  work  of  Cope,  Marsh,  and 
Huxley  has  been  so  careful  and  painstaking,  and 
has  been  attended  with  so  much  success,  that  the 
actual  history  of  many  of  our  vertebrates  has  been 
accurately  traced  from  fossil  specimens. 

It  is  interesting  to  compare  the  state  of  our 
knowledge  to-day  as  to  these  intermediate  types, 
with  that  which  the  first  edition  of  the  "  Origin  of 


DISCOVERIES  OF   CONNECTING  LINKS.        1 09 

Species  "  could  bring  to  its  aid.  A  few  synthetic 
types  were  at  that  time  known  ;  but  they  were  so 
little  understood  as  to  have  no  particular  meaning. 
Darwin,  realizing  as  he  did  that  one  of  the  weakest 
points  in  his  theory  was  the  impossibility  of  finding 
the  many  links  which  it  demanded,  was  only  able 
in  the  first  edition  of  his  book  to  claim  that  Owen 
had  shown  that  Ruminants  and  Pachyderms  were 
connected  by  fossils.  To-day  it  would  take  pages 
to  enumerate  the  different  fossils  found  to  connect, 
in  a  more  or  less  direct  manner,  the  living  with  ex- 
tinct animals  and  with  each  other. 

It  may,  perhaps,  be  well  to  mention  a  few  of  these 
instances.  The  best-known  history  is  that  of  the 
horse  family.  The  earliest  representative  was  the 
eohippus  of  the  Eocene  rocks,  which  had  on  its  fore 
feet  the  representations  of  five  toes,  and  was  a  small 
animal  about  the  size  of  a  fox.  From  this  starting- 
point  the  history  has  been  carefully  followed.  The 
animal  becomes  larger ;  it  loses  one  toe,  then  a 
second  ;  and  coming  on  later,  two  of  the  three  re- 
maining toes  become  smaller,  and  finally  all  that  is 
left  of  them  are  the  so-called  splint  bones.  Accom- 
panying these  changes  are  others,  so  that  almost 
every  step  in  the  history  of  this  family  from  its  five- 
toed  ancestor,  is  known.  And  not  only  this,  but 
the  even-toed  Ungulates  have  been  similarly  traced 
back  to  a  five-toed  ancestor.  Indeed,  by  means  of 
the  numerous  fossils  found  of  late  years,  almost  all 
of  the  orders  of  mammals  have  been  traced  back- 
wards by  converging  lines.  And  Cope  has  dis- 
covered a  very  early  animal  which  presents  such 


IIO  E  VOL  UTION  OF  TO-DA  F. 

generalized  characteristics  that  he  considers  it  as 
representing  the  common  ancestor  of  all  true  mam- 
malia, and  has  named  the  group  the  Condylarthra. 
The  number  of  connecting  links  uniting  this  animal 
with  the  modern  orders  is  very  great.  Still  earlier 
is  found  a  series  of  fossils  uniting  birds  and  reptiles. 
These  classes,  in  their  anatomy,  show  a  close  rela- 
tionship, and  they  have  been  united  in  a  surprising 
manner  by  fossils.  The  world-renowned  Arche- 
opteryx  and  the  remarkable  Odontornithes,  the 
toothed  birds  of  the  American  Cretaceous,  are  reptile- 
like  birds ;  while  the  Composgnathus  seems  to  be  a 
bird-like  reptile.  Indeed,  so  successful  have  been 
the  researches  upon  fossil  vertebrates,  that  Cope, 
who  has  studied  the  subject  with  great  care,  thinks 
that  they  have  "  disclosed  the  ancestry  of  the  mam- 
mals, the  birds,  the  reptiles,  and  the  true  fishes," 
and  he  unhesitatingly  gives  a  phylogenetic  history 
of  the  whole  vertebrate  sub-kingdom.  Whether  this 
history,  as  given  by  Cope,  be  right  or  wrong,  does 
not,  however,  concern  us  ;  the  very  fact  that  it  is 
possible  to  make  such  a  history  from  the  study  of 
fossils,  shows  what  a  great  advance  has  been  made 
in  the  direction  of  finding  links,  since  the  matter 
has  been  subject  to  careful  investigation  under  the 
inspiration  of  the  "  Origin  of  Species." 

It  is  hardly  possible  to  exaggerate  the  importance 
of  this  result.  From  the  very  first  the  absence  of 
these  connecting  species  has  been  recognized  as  a 
most  serious  obstacle  for  evolution.  But,  as  year 
by  year  goes  by,  fresh  discoveries  have  been  con- 
tinually bringing  to  light  instance  after  instance 


DISCOVERIES  OF  CONNECTING  LINKS.        Ill 

of  these  types  of  union,  until  the  difficulty  has  not 
only  disappeared,  but  has  been  turned  into  a  very 
cogent  positive  argument. 

One  very  important  feature  in  regard  to  these 
connecting  links  is  the  geological  position  in  which 
they  are  found.  A  connecting  link  ought  to  appear 
before  the  two  forms  which  it  connects,  or  some- 
times between  them.  The  former  position  is  the 
more  natural  one,  and  a  synthetic  form  in  this  posi- 
tion is  understood  to  be  the  common  ancestor  of 
the  later  groups  which  it  connects.  Most  of  our 
fossils  are  of  this  character,  being  anatomically 
intercalated  between  existing  groups,  and  always 
occurring  at  earlier  periods.  The  second  position 
might  sometimes  occur,  and  would  be  explained  by 
supposing  the  fossil  in  question  represented  a  tran- 
sitional stage  between  the  earlier  and  the  later 
groups  which  it  connects.  The  occurrence  of  a 
connecting  link  later  than  the  animals  connected 
by  it,  would  be,  according  to  the  descent  theory, 
surprising,  and  only  explained  by  supposing  that  it 
originally  appeared  earlier,  but  left  no  trace  of  itself, 
while  some  individual  survivor,  in  after-ages,  did 
happen  to  be  preserved  as  a  fossil.  And  this  expla- 
nation would  evidently  only  apply  to  sporadic  cases. 
Now,  the  universal  rule  is,  that  true  connecting 
links  occupy  one  of  the  first  two  positions,  and 
never  the  last.  The  successive  fossils  which  connect 
the  horse  family  with  the  ancient  five-toed  ancestor 
occur  in  successively  lower  and  lower  rocks ;  while 
the  forms  connecting  this  family  with  the  even- 
toed  Ungulates  occur  still  lower  down.  Indeed,  I 


112  E  VOL  UTION  OF  TO-DA  Y. 

can  find  no  instance  where  a  true  fossil  connecting- 
link  appears  later  than  the  groups  connected  by  it. 
In  short,  the  geological  location  of  fossils  is  exactly 
that  which  the  theory  of  descent  would  lead  us  to 
expect. 

For  reasons  already  considered,  the  number  of 
synthetic  forms  found  among  invertebrate  fossils  is 
not  so  great  as  that  of  the  vertebrates.  But  still 
they  are  not  absent,  though  they  are  few  and  scat- 
tering. It  is  not  possible  in  any  case  among  inver- 
tebrates to  build  a  connected  history  such  as  we 
have  seen  can  be  done  with  some  vertebrate  fami- 
lies. The  scattered  connecting  forms  only  enable 
us  to  get  a  hint  here  and  there  as  to  the  probable 
development.  The  Crustacea  form  an  interesting 
group.  The  existing  crabs  can  be  traced  back 
through  various  simple  form  to  the  Oolitic  rocks, 
where  they  seem  to  merge  into  the  less  highly  devel- 
oped group  Anomoura,  a  group  in  many  respects  in- 
termediate between  them  and  the  Macroura  (lobsters 
and  shrimps).  Still  further  back  the  Anomoura  dis- 
appear, and  the  group  of  Macroura  take  their  place 
in  the  Carboniferous.  And  still  earlier  these  are 
united  to  the  Phyllopods  by  Silurian  forms  (Ceratro- 
caris).  In  another  line  the  ancient  Euryperids  are 
united  to  the  family  to  which  the  king-crab  belongs, 
by  a  fossil  called  Hemiaspis,  while  the  king-crabs  are 
united  to  the  ancient  Trilobdes  by  another  fossil 
(PrestwichSa).  Alexander  Agassiz  has  very  carefully 
studied  the  whole  series  of  fossil  forms  of  sea- 
urchins.  From  the  fact  that  the  classes  of  this  group 
were  already  differentiated  in  the  Silurian  age,  it 


DISCOVERIES  OF  CONNECTING  LINKS.        113 

was,  of  course,  impossible  to  discover  connecting 
links  between  them  ;  but  he  had  no  difficulty  in 
discovering  a  continuity  between  the  Silurian  Echin- 
oderms  and  the  existing  forms,  and  thus  to  show 
that  the  present  forms  are  descendants  from  the 
ancient  fossil  families.  He  was  not  able  to  trace 
the  history  of  the  successive  genera,  but  easily  made 
out  a  general  slow  modification. 

But  there  is  no  need  of  multiplying  examples. 
The  full  force  of  the  argument  can  only  appear 
by  a  long  and  careful  consideration  of  special  cases, 
and  this  lies  beyond  the  scope  of  this  work.  Un- 
doubtedly the  tendency  of  recent  advances  in  pale- 
ontology is  to  fill  in  the  gaps  between  large  numbers 
of  our  present  widely  separated  groups.  Particu- 
larly is  this  true  of  vertebrates,  and  inasmuch  as 
it  is  this  group  alone  that  has  left  behind  it  any 
thing  like  a  satisfactory  history,  it  must  be  to  this 
group  that  most  of  our  future  discoveries  will  be 
confined. 

Undoubtedly  many  of  the  so-called  connecting 
links  which  have  been  described  are  not  what  is 
claimed  for  them.  Imbued  with  the  evolutionary 
belief,  our  paleontologists  are  everywhere  in  hunt 
for  these  links,  and  will  be  quite  apt  to  find  such 
links  in  animals  where  analogical  likeness  is  all  that 
exists.  The  various  histories  drawn  from  paleonto- 
logical  evidence  may  be  in  error  at  many  points. 
But  making  all  allowance  for  these  errors,  there  can 
be  no  questioning  the  statement  that  the  last  twenty 
years  have  added  so  much  to  our  knowledge  of  the 
connected  history  of  vertebrates  in  the  past,  as  to 


114  EVOLUTION  OF  TO-DA  Y. 

justify  the  statement  that  the  fossil  history  since  the 
Silurian  age  is  in  strict  accordance  with  what  we 
should  expect  to  find  according  to  the  theory  of 
evolution.  Scientists  to-day  who  have  carefully 
studied  the  subject,  claim  that  paleontology  practi- 
cally demonstrates  the  derivative  origin  of  species. 
It  shows  as  far  as  it  is  possible  to  be  shown  that  our 
fauna  is  derived  from  that  of  the  geological  ages ; 
our  classes  being  descendants  of  the  older  general- 
ized forms,  our  families  from  later  types,  and  our 
species  from  the  very  recent  branches  of  the  later 
divisions. 

The  Development  of  tlie  Brain  in  Mammals. 

One  very  interesting  result  has  appeared  from  the 
work  of  Marsh  upon  tertiary  mammals  in  regard  to 
the  growth  of  the  brain.  To  give  his  own  summary  : 
(i)  All  tertiary  mammals  had  small  brains.  (2) 
There  was  a  gradual  increase  in  the  size  of  the 
brain  during  this  period.  (3)  The  increase  was 
mainly  confined  to  the  cerebral  hemispheres  or 
higher  portions  of  the  brain.  (4)  In  some  groups 
the  convolutions  of  the  brain  have  gradually  become 
complicated.  (5)  In  some  the  cerebellum  and 
olfactory  lobes  have  diminished  in  size.  These  are 
very  significant  results  when  we  consider  the  enor- 
mous size  of  many  of  the  older  animals  and  the 
comparative  small  size  of  the  modern  ones.  It  ap- 
pears that  till  the  time  of  the  appearance  of  mam- 
mals the  struggle  for  existence  had  been  confined 
to  physical  superiority  ;  but  that,  with  the  beginning 
of  the  Tertiary,  a  new  era  ensued,  resulting  in  the 


PALEOBOTANY.  11$ 

growth  of  the  brain,  and  from  that  time  the  contest 
has  been  one  of  intelligence. 

Paleobotany. 

The  fossil  history  of  plants  has  not  been  so  much 
studied  as  that  of  animals,  and  much  less  is  known 
about  it  ;  or  at  all  events  it  has  given  less  important 
results.  Plants  are  not  so  easily  preserved  as  animals 
with  hard  parts,  and  while  from  a  few  specimens  it  is 
known  that  an  abundant  flora  existed  even  in  the 
Silurian  era,  the  record  is  very  meagre.  In  general, 
paleobotany  offers  somewhat  the  same  sort  of  testi- 
mony as  that  which  we  have  examined  above.  The 
plants  of  the  Silurian,  however,  present  no  such  diffi- 
culties as  do  the  animals,  chiefly  perhaps  because  so 
little  is  known  about  them.  They  constitute  a  quite 
well  developed  flora  of  Algae,  Sigillaroids,  Lycopods, 
ferns,  and  Equisitacea,  all  plants  of  undoubted  low 
scale  of  organization.  Conifers  make  their  appear- 
ance next,  in  the  Devonian,  and  Dawson  claims  to 
have  found  here  an  angiosperm.  This  claim  is  more 
than  doubtful,  however,  and  the  Devonian  is  on  the 
whole  characterized  by  Cryptogams  and  Gymno- 
sperms.  This  flora  passed  directly  over  into  the 
profuse  vegetation  of  the  Carboniferous  age,  with 
little  change,  nearly  all  of  the  genera  of  the  one 
period  being  found  in  the  other,  though  few  of  the 
species  are  common  to  the  two.  At  this  time  also 
Monocotyledons  made  their  appearance.  With  the 
beginning  of  the  Mezozoic  the  Cycads  are  expanded, 
while  the  peculiar  carboniferous  forms  are  disap- 
pearing. In  the  upper  Cretaceous  rocks  finally  ap- 


Il6  EVOLUTION  OF  TO-DAY. 

pear  the  Dicotyledons,  and  the  modern  forest-trees 
can  be  traced  back  to  this  time. 

It  will  be  seen  that  this  history  represents  a  contin- 
ual advance  :  first,  Cryptogams,  then  Gymnosperms, 
Monocotyledons,  and  Dicotyledons,  in  consecutive 
order.  But  no  such  minute  histories  have  been 
traced  here  as  we  have  seen  in  the  animal  kingdom. 
The  most  remarkable  feature  of  paleobotany,  and 
the  only  one  which  offers  any  serious  difficulty,  is 
the  appearance  of  dicotyledonous  angiosperms  in 
the  upper  Cretaceous.  In  Western  North  America 
is  found  a  vast  bed  of  rocks  known  as  the  Dakota 
formation,  whose  age  is  by  some  high  authorities 
considered  as  lower  Cretaceous,  and  by  others  as  up- 
per Tertiary.  Whichever  it  may  be  it  is  a  fact  that 
here  suddenly  appear  the  highest  plants.  Previous 
to  this  time  no  Dicotyledons  are  known  to  have  ex- 
isted, but  here  abruptly  appear  in  a  perfect  condi- 
tion a  flora  almost  exactly  agreeing  with  the  flora  of 
to-day.  There  were  oaks,  poplars,  magnolias,  ma- 
ples, beeches,  elms,  firs,  hollies,  and  hosts  of  other 
modern  plants,  agreeing,  as  far  as  can  be  judged 
from  leaves,  even  to  the  species,  with  those  now 
existing.  Indeed  the  forest  of  this  period  must 
have  borne  an  almost  exact  resemblance  to  the 
forests  of  to-day.  The  sudden  appearance  of  such 
a  remarkably  diversified  flora,  and  the  fact  that  it 
has  since  that  time  remained  almost  unchanged,  are 
two  great  difficulties  for  evolution  to  meet.  The 
first  can  only  be  met  by  appealing  to  the  imperfec- 
tion of  the  record.  To  the  second  difficulty  it  may 
be  suggested,  that  the  group  of  plants,  once  de- 


SUMMARY.  117 

veloped,  so  well  fitted  its  place  in  nature  that  further 
change  would  be  unnecessary,  unless  some  change  in 
conditions  should  arise.  This  is,  however,  only  a 
suggestion,  not  an  explanation. 

Summary. 

"It  must  be  conceded  that,  on  the  whole,  the 
testimony  of  the  rocks  is  in  favor  of  the  doc- 
trine of  evolution,"  is  the  decision  of  the  most 
advanced  geologists  to-day.  Undoubtedly  there 
are  many  difficulties  in  the  way,  and  very  seri- 
ous some  of  them  are,  which  yet  remain  unan- 
swered. The  sudden  appearance  of  such  a  highly 
differentiated  fauna  at  the  very  base  of  the  Silurian, 
and  the  character  of  this  fauna,  consisting,  as  it  did, 
of  all  of  the  sub-kingdoms,  are  facts  which  are 
unfortunate  for  the  evolution  theory ;  for,  if  they 
do  nothing  else,  they  make  it  utterly  impossible  to 
show  that  the  great  types  are  related  to  each  other 
by  converging  lines.  The  absence  of  life  in  rocks 
older  than  the  Silurian,  shrouds  in  absolute  darkness 
the  origin  of  the  various  sub-kingdoms  and  classes, 
for  at  the  very  first  glimpse  we  have  of  life  they 
were  as  widely  apart  as  they  are  now.  The  result 
of  careful  research,  which  tends  to  show  that  a  very 
large  majority  of  our  orders,  sub-orders  and  families 
can  be  traced  back  to  these  early  times,  makes  it 
still  more  difficult  to  recognize  converging  lines,  and 
confines  the  search  chiefly  to  the  one  group  of  ver- 
tebrates which  has  developed  since  that  time.  The 
occasional  survival  of  some  forms  almost  unmodi- 
fied through  the  enormous  geological  ages  ;  the  great 


1 1 8  E  VOL  UTION  OF  TO-DA  Y. 

preponderance  of  specialized  forms  at  all  times  over 
generalized  types,  which  the  descent  theory  assumes 
have  existed ;  the  sudden  appearance  of  various 
highly-developed  groups  of  animals  and  plants  in 
later  times,  such  as  the  Teleost  fishes  and  the  Di- 
cotyledonous plants  abruptly  in  the  Cretaceous  with 
absolutely  no  previous  indications  of  their  exist- 
ence; the  discrepancies  as  to  the  necessary  amount 
of  time  required  for  the  development  of  the  animal 
kingdom,  as  estimated  by  Darwin,  and  the  probable 
age  of  the  world  as  estimated  by  Sir  William  Thom- 
son and  others ; — all  of  these  difficulties,  though 
partially  answered  and  certainly  not  unsurmountable, 
still  demand  the  attention  of  our  scientists. 

On  the  other  hand,  the  researches  since  Darwin 
have  proved  that  our  paleontological  record  is  very 
imperfect,  particularly  at  its  beginning,  where  most 
of  the  difficulties  occur,  and  with  this  conclusion 
many  of  them  disappear.  "  As  the  area  over  which 
accurate  observations  have  been  carried  on  extends, 
and  as  fossiliferous  rocks  found  in  one  locality  fill 
up  the  gaps  left  in  another,  the  abrupt  demarkations 
between  the  fauna  and  flora  of  different  epochs  dis- 
appear," and  in  numerous  cases  fossils  have  been 
found  to  bridge  over  the  gaps  existing  between 
widely  different  groups.  The  patient  study  of 
vertebrate  fossils,  which  have  left  the  most  com- 
plete record,  has  given  a  very  exact  history  of  their 
development,  a  history  becoming  more  and  more 
complete  with  the  discovery  of  every  new  fossil. 
The  accumulation  of  the  numerous  links  connecting 
animals,  and  the  satisfactory  explanation  which  evolu- 


SUMMARY.  119 

tion  gives  to  every  newly  discovered  fact,  the 
exactness  with  which  the  new  fossils  fall  into  their 
places,  both  as  regards  their  structure  and  the  time 
at  which  they  lived,  have  all  together  led  paleon- 
tologists, as  a  rule,  to  conclude  that  the  positive 
evidence  is  sufficient  to  outweigh  the  numerous  dif- 
ficulties, and  indicate  that  the  history  of  animals 
has  been  an  evolutionary  one  of  some  form. 


CHAPTER  IV. 

EMBRYOLOGY. 

The  Importance  of  Embryology. 

THE  evidence  which  organic  evolution  derives 
from  classification  and  geological  succession  is  as 
conclusive  as  could  be  expected  from  such  data. 
The  genetic  connection  of  animals  is,  however,  only 
a  matter  of  inference,  if  this  evidence  only  be  con. 
sidered  ;  a  very  strong  inference  it  is  to  be  sure,  but 
one  which  does  not  necessarily  follow  from  the  facts. 
It  is  always  possible  to  say,  and  frequently  has  been 
claimed,  that  although  animals  are  classified  as  if 
genetically -related,  and  although  the  fossils  appear 
in  order  exactly  in  harmony  with  the  same  idea,  yet 
there  is  no  proof  that  the  species  thus  appearing  did 
develop  from  each  other.  It  is  possible  to  admit  all 
of  the  facts  which  we  have  hitherto  considered,  and 
still  to  claim  that  it  has  only  been  shown  that  if 
evolution  were  true,  classification  and  paleontology 
would  be  as  we  find  them,  but  that  no  direct  argu- 
ment has  been  offered  to  prove  that  the  species  liv- 
ing to-day  have  passed  through  these  various  early 
stages.  Direct  proof  of  genetic  descent  of  the  nature 
demanded  by  this  claim  is  impossible,  but  the  infer- 
ences from  the  classes  of  facts  considered  is  the 


THE  IMPORTANCE   OF  EMBRYOLOGY.          121 

present  chapter  and  the  next  are  somewhat  differ- 
ent in  their  nature  from  those  already  considered, 
and  bear  more  directly  on  the  question  of  genetic 
descent. 

When  the  "  Origin  of  Species  "  was  written,  its  au- 
thor did  not  realize  the  great  aid  his  views  were  to 
receive  from  the  study  of  embryology,  and  the  sub- 
ject was  passed  over  by  him  in  a  manner  which 
to  the  scientists  of  to-day  seems  entirely  unsatis- 
factory for  such  an  important  subject.  But  this 
source  of  evidence  did  not  exist  at  the  time  the 
"  Origin  of  Species  "  was  written,  for  embryology  as 
a  science  is  of  later  date.  A  few  embryological  facts 
had  at  that  time  been  collected,  and  the  generaliza- 
tions of  Von  Baer  and  Rathke  had  laid  the  founda- 
tion of  what  has  since  become  a  science.  It  was  im- 
possible to  appreciate  the  significance  of  the  facts 
until  evolution  was  sought  as  an  interpretation.  As 
soon  as  this  theory  began  to  be  seriously  discussed, 
it  became  evident  that  along  the  line  of  embryology 
might  be  expected  the  most  cogent  arguments  upon 
the  question. 

Nor  has  this  expectation  proved  delusive,  for  the 
evidence  here  afforded  has  been  perhaps  the  most 
important  factor  in  leading  modern  scientists  to  ac- 
cept evolution.  Although  embryology  was  only 
slightly  considered  by  Darwin,  either  in  the  earlier 
or  later  additions  of  his  book,  the  subject  soon  ob- 
tained able  exponents.  Spencer  and  Haeckel,  with 
an  immediate  perception  of  the  significance  of  the 
subject,  treated  it  ensemble,  and  deduced  from  the 
then  imperfectly  known  facts  some  brilliant  gener- 


122  EVOLUTION  OF  TO-DAY. 

alizations,  which  have  been  the  guiding  principles  of 
embryologists  ever  since.  Spencer  contented  him- 
self with  pointing  out  the  general  principles  con- 
nected with  embryology  in  its  relation  to  evolu- 
tion ;  and  so  well  taken  were  his  deductions  that 
most  of  them  will  stand  to-day  as  he  wrote  them 
twenty  years'  ago.  Haeckel  did  not  stop  here, 
but  having  recognized  the  underlying  principles,  at- 
tempted to  apply  them  to  special  cases  ;  and  be- 
cause his  data  were  then  scanty  he  was  led  into 
many  erroneous  conclusions.  He  attempted  at 
that  time  to  do  more  than  embryologists,  with  all 
their  advance  in  knowledge,  consider  themselves 
able  to  do  to-day. 

Embryology  a  Repetition  of  Past  History. 

The  fundamental  principle  which  underlies  all 
modern  research  in  this  direction,  is  simply  the  as- 
sumption that  the  development  of  the  individual 
repeats  briefly  the  development  of  the  race ;  that  if 
we  could  trace  perfectly  the  development  of  any 
animal  from  the  egg,  we  should  thus  get  an  epito- 
mized history  of  the  development  of  the  race  to 
which  the  animal  in  question  belongs,  through  the 
countless  ages  of  the  past.  The  great  significance 
of  this  assumption  is  at  once  evident.  If  true,  it 
gives  the  student,  with  his  microscope  and  section 
instrument,  the  opportunity  of  studying  in  the 
laboratory  the  past  history  of  animals,  of  discover- 
ing thus  the  exact  blood-relationship  of  animals  to 
each  other,  and  thus  explaining  most  of  the  anom- 
alies of  classification.  In  short,  if  embryology  is 


REPETITION  OF  PAST  HISTORY.  12$ 

a  summary  of  past  history,  it  is  a  key  to  the  prob- 
lem of  the  origin  of  the  animal  kingdom  as  it  exists 
to-day. 

For  the  pursuance  of  this  study  three  tasks  are 
necessary:  (i)  We  must  discover  whether  or  not 
this  assumption  is  true  ;  (2)  we  must  find,  if  possi- 
ble, an  explanation  of  the  fact,  if  its  truth  is  demon- 
strated ;  and  (3)  we  must  apply  the  principle  in 
every  conceivable  direction,  and  construct,  as  far  as 
possible,  the  history  of  the  animal  kingdom,  in  order 
to  discover  if  the  result  be  in  harmony  with  the  evi- 
dence from  other  sources.  A  perfectly  satisfactory 
answer  cannot  as  yet  be  given  to  any  of  these  ques- 
tions ;  but  the  evidence  is  daily  increasing,  and  it  is 
not  difficult  to  see  what  the  final  result  will  be. 

I. — As  to  the  Truth  of  the  Assumption  that  Embry- 
ology Repeats  Past  History. 

Several  methods  of  investigation  are  here  possible. 
The  simplest,  and  the  one  most  readily  suggesting 
itself,  is  to  compare  the  history  of  animals  as  taught 
by  embryology  with  their  history  as  taught  by  fos- 
sils. If  it  could  be  shown  that  the  two  agree  per- 
fectly, we  should  have  a  demonstration  of  the  point. 
But  this  is  obviously  at  present  impossible.  Such 
an  exact  comparison  can  only  be  made  when  we 
have  complete,  both  the  fossil  and  embryological 
history  of  all  animals,  and  our  knowledge  of  both  of 
these  subjects  is  as  yet  very  imperfect.  That  there 
is  a  general  parallelism  between  the  two  is  every- 
where acknowledged  ;  indeed,  it  was  recognized  half 
a  century  ago  to  its  fullest  extent  by  Louis  Agassiz. 


1 24  E  VOL  UTION  OF  TO-DA  Y. 

He  plainly  saw  the  principle,  and  used  it  as  an  argu- 
ment in  his  essay  on  classification.  The  embryo 
everywhere  begins  as  a  simple  undifferentiated 
organism,  and  builds  itself  up  through  successively 
higher  and  higher  grades,  until  it  finally  reaches  the 
complicated  adult.  And  so  in  fossil  history  it  ap- 
pears, rather  indefinitely  and  yet  distinctly,  that 
the  lower  forms  appear  in  the  earlier  ages,  and  give 
place  as  the  ages  go  by  to  successively  higher  and 
higher  forms,  until  the  most  complicated  appear 
last.  But  such  a  general  parallelism  as  this  has  no 
meaning,  and,  unless  more  definite  evidence  can  be 
found,  our  assumption  is  of  no  importance. 

But  if  we  cease  to  make  the  question  quite  so 
broad  and  confine  it  to  special  cases,  we  may  per- 
haps get  more  definite  conclusions.  And  here  we 
labor  under  the  disadvantage  that,  for  reasons  that 
we  shall  see  later,  the  vertebrates  which  have  the 
most  complete  fossil  history  have  the  most  incom- 
plete embryological  history.  The  only  systematic 
attempt  at  such  a  comparison  as  we  are  considering, 
has  been  made  by  A.  Agassiz.  Having  at  his  com- 
mand a  great  number  of  fossil  echinoids,  he  has 
made  a  very  careful  study  of  them  for  the  purpose 
of  discovering  how  accurately  a  parallel  could  be 
drawn  between  their  history  and  that  of  the  young 
echinoid.  The  result  of  this  comparison  was  to  sub- 
stantiate the  theory  in  its  general  bearings.  "  We 
are  justified,"  he  says,  "  in  seeking  for  our  earliest 
representative  of  the  order  such  echinoderms  as 
resemble  early  stages  of  our  embryos."  But  he  con- 
cludes further  that  "  any  thing  beyond  a  general 


REPETITION  OF  PAST  HISTORY.  12$ 

parallelism  is  hopeless."  It  may  be  possible,  he 
thinks,  to  decide  as  to  the  general  line  along  which 
echinoderms  have  developed,  but  any  attempt  to 
trace  the  history  of  genera  in  this  way  will  only 
result  in  complete  failure.  Embryology  alone  is  not 
a  safe  guide,  and  only  so  far  as  it  is  possible  to  verify 
it  by  actual  fossils,  can  it  with  justice  be  relied  upon 
as  giving  any  thing  more  than  a  general  history  of 
the  past.  The  parallelism  exists,  but  our  power  of 
interpreting  it  is  not  great.  This  conclusion  as  to 
limiting  the  use  of  embryology  in  teaching  history, 
has  naturally  been  a  disappointment  to  the  enthusi- 
astic embryologists,  who  have  not  hesitated  to  say 
that  the  work  of  Agassiz  marks  a  step  backward. 
But  it  is  certainly  a  wholesome  check  to  the  too  pre- 
cipitous advance  in  this  direction  ;  for  the  embryolo- 
gist  has  begun  to  rank  his  science  too  highly,  a 
common  fault  with  all  specialists.  But  whatever  be 
the  result  obtained  by  Agassiz  as  to  our  power  of 
following  this  parallelism,  there  was  no  question  on 
his  part  that  such  a  general  parallelism  does  exist. 

Beyond  this  work  of  Agassiz,  there  has  been  rto 
thorough  attempt  to  investigate  the  matter.  It 
is  so  difficult  to  obtain  a  sufficient  amount  of  fos- 
sil material  to  make  a  satisfactory  parallel,  that 
none  have  had  the  courage  to  attempt  it.  Of  course, 
from  the  fact  that  the  assumption  has  been  so  con- 
stantly in  the  minds  of  scientists,  it  has  followed  that 
vast  numbers  of  disjointed  facts  have  been  noticed 
bearing  on  the  point.  Usually  the  investigator  has 
satisfied  himself  with  observing  a  few  isolated  facts, 
and  saying  that  they  form  another  instance  of  the 


126  EVOLUTION  OF  TO-DAY. 

well-known  parallelism  between  embryology  and 
paleontology.  There  is  hardly  a  class  in  which 
some  such  parallelism  cannot  be  distinctly  shown, 
and  many  instances  are  very  striking.  It  is  seen 
among  the  mollusks,  particularly  in  the  class  Cephal- 
opoda ;  it  is  seen  among  the  Crustacea,  the  Decapods 
showing  very  beautifully  a  paleontological  develop- 
ment agreeing  with  their  embryology.  Vertebrates, 
perhaps,  give  the  best  illustrations  of  all,  as  can  be 
seen  by  examining  the  various  works  on  fossil  ver- 
tebrates, from  the  time  of  Louis  Agassiz  until  now. 
When,  therefore,  we  take  all  of  the  facts  together,  see- 
ing that  with  our  imperfect  knowledge  of  fossils  we 
find  a  general  parallel  everywhere  expressed,  we  can 
safely  say  that  the  investigations  of  the  last  twenty 
years  in  paleontology  have  been  slowly  but  per- 
sistently strengthening  the  belief  in  the  truth  of  the 
hypothesis.  While  the  evidence  is  scanty,  it  all 
bears  in  one  direction. 

Embryology  Compared  with  a  Hypothetical  History. 

Fossils  are  too  scanty,  and  paleontological  evi- 
dence has  been  hitherto  too  imperfect,  for  a  demon- 
stration of  the  truth  of  the  hypothesis.  It  is 
necessary,  therefore,  to  search  for  proof  in  some 
other  direction.  One  method  of  doing  this  is  to 
compare  embryology  with  the  hypothetical  history 
which  the  study  of  adult  forms  with  their  relations 
to  each  other  would  lead  us  to  construct.  If  the 
two  agree,  we  may  rest  assured  of  the  truth  of  the 
hypothesis;  if  they  disagree,  something  must  be 
wrong.  Two  species  of  the  same  genus  must,  ac- 


EMBRYOLOGY  AND  HYPOTHETICAL  HISTORY.    I2/ 

cording  to  the  descent  theory,  have  had  precisely 
the  same  history  until  comparatively  recent  times. 
Genera  of  the  same  family  separated  from  each 
other  at  an  earlier  period,  and  families  of  the  same 
order  at  still  more  remote  times,  while  the  different 
sub-kingdoms  have  had  no  common  history  since 
the  earliest  ages.  If,  now,  embryology  were  an 
exact  repetition  of  past  history,  we  should  expect 
to  find  the  development  of  individuals  of  related 
species  agreeing  except  in  the  very  latest  stages. 
Genera  would  show  a  similarity  of  development  not 
quite  so  long,  families  and  orders  would  separate 
from  each  other  still  earlier,  while  the  sub-kingdoms 
would  show  no  similarity  except  in  the  earliest 
stages.  Every  two  animals  should  begin  their  de- 
velopment alike,  and  the  point  at  which  they  become 
unlike  would  depend  upon  the  closeness  of  their 
genetic  relation. 

Around  this  point  has  centred  a  large  part  of 
modern  embryological  research.  Not  always,  per- 
haps, realizing  the  significance  of  their  results, 
naturalists  have  been  trying  to  make  the  various 
facts  collected  harmonize  with  each  other.  For  it 
is  almost  immediately  recognized,  was  indeed  recog- 
nized by  Spencer  and  Haeckel,  that  the  embryo- 
logical  history  of  animals  is  not  in  strict  harmony 
with  their  relations  to  each  other.  Two  animals 
quite  closely  related  in  adult  anatomy,  may 
have  embryological  histories  differing  very  widely 
from  each  other  from  the  very  first  stages.  The 
embryology  of  the  genera  of  a  single  family  does 
not  always  represent  a  unity,  although  as  a  rule  it 


128  E  VOL  U  T/ON  OF  TO-DA  Y. 

does.  Two  annelids  may  be  selected,  agreeing 
quite  closely  in  adult  anatomy,  but  whose  develop- 
ment shows  no  likeness  until  the  latest  stages  are 
reached.  Of  course  these  annelids  must  have  had 
practically  the  same  past  history,  if  the  descent  the- 
ory is  true,  and  the  fact  that  their  embryology  is  so 
very  different,  seems  at  first  sight  to  disprove  that 
the  one  is  the  re'sume'  of  the  other. 

But  upon  more  careful  investigation  it  has  ap- 
peared that  these  seeming  contradictions  form  per- 
haps the  strongest  argument  in  support  of  the 
hypothesis.  In  the  first  place,  it  has  been  more  and 
more  evident  with  advancing  knowledge  that,  al- 
though small  groups  may  show  irregularities,  as 
a  rule,  embryology  is  in  harmony  with  such  hypo- 
thetical history,  and  is  as  a  whole  a  unity.  The 
same  principles  apply  everywhere,  and  facts  are 
daily  being  brought  to  light  showing  that  harmony 
is  to  be  the  final  result.  So  convinced  have  been 
embryologists  of  the  truth  of  this  fundamental 
principle,  that  the  presence  of  the  seeming  contra- 
dictions has  caused  no  hesitation.  They  have  only 
regarded  them  as  obstacles  to  be  overcome. 

Method  of  Explaining  the  Contradictions. 

In  most  cases  these  contradictions  have  been  ex- 
plained in  a  satisfactory  manner,  though  some  still 
await  further  discoveries  before  they  can  be  made 
clear.  The  general  line  of  argument  which  has  been 
used  to  meet  the  difficulties  is  somewhat  as  follows : 
Assuming  the  law  to  be  that  embryology  should  re- 
peat past  history,  an  assumption  supported  by  the 


EXPLAINING  THE   CONTRADICTIONS.  129 

majority  of  the  evidence,  the  question  is  asked 
whether  some  valid  reason  cannot  be  given  why  this 
law  should  in  certain  cases  be  departed  from.  An 
answer  is  soon  found  in  the  influence  of  the  sur- 
roundings of  the  embryo,  which  sometimes  prevent 
the  normal  course  from  being  followed.  By  its  own 
innate  tendency  the  embryo  would  follow  the  line 
of  ancestral  history,  but  while  going  through  its  de- 
velopment it  is  placed  under  circumstances  which 
render  this  impossible.  In  such  cases  the  history  is 
shortened,  either  from  necessity  or  to  cut  short  the 
embryonic  period,  which  is  the  period  of  greatest 
helplessness.  As  an  illustration  of  the  principle, 
let  us  consider  the  -ordinary  earthworm  (annelid). 
Among  other  peculiarities,  we  find  that  its  embryo 
possesses  for  a  long  time  no  mouth  or  digestive 
canal.  This  fact  is  in  itself  proof  that  embryology 
may  depart  from  past  history,  for  the  ancestors  of 
the  annelid  must  at  all  times  have  possessed  a  mouth 
and  digestive  tract,  or  they  could  not  have  lived. 
The  embryo  unquestionably  departs  from  this  his- 
tory, and  a  reason  for  it  is  found  in  a  very  simple 
fact.  The  use  of  the  mouth  and  digestive  tract  is 
to  supply  the  animal  with  food.  But  our  modern 
annelid  embryo  is  not  required  to  collect  food,  for  it 
has  a  supply  already  at  hand.  The  egg  within 
which  the  embryo  develops  contains  a  large  store  of 
food  already  prepared  to  enter  into  the  body  of  the 
embryo,  and  therefore  the  presence  of  a  mouth  and 
digestive  tract  is  unnecessary  until  a  much  later 
period  when  the  food  is  used.  And  not  only  this,  but 
the  food-yolk  is  so  bulky  that  it  fills  the  whole  space 


1 30  E  VOL  UTION  OF  TO-DA  Y. 

where  the  digestive  canal  ought  to  be,  and  thus  by 
its  simple  bulk  effectually  prevents  the  regular  for- 
mation of  these  organs.  The  embryo  does  seem  to 
try,  even  here,  to  follow  the  primitive  history,  for  it 
develops  a  mouth  in  a  roundabout  way,  and  separ- 
ates off  cells  which  correspond  to  the  digestive  tract. 
But  the  mouth  frequently  closes  up,  since  it  is  of  no 
use,  and  the  presence  of  the  bulky  food  prevents 
the  alimentary  canal  from  being  formed.  After  the 
food  is  used  up  the  mouth  again  appears,  the  ali- 
mentary canal  becomes  functional,  and  the  typical 
history  is  once  more  resumed.  In  other  words,  the 
embryo  attempts  to  follow  the  line  of  ancestral  his- 
tory, but  the  presence  of  food  makes  this  impossi- 
ble, and  as  a  result  some  of  the  history  is  skipped. 
If  now  it  be  possible  to  find  another  annelid  in 
which  no  food  is  stored  up  in  the  egg,  evidently 
these  modifying  conditions  will  be  absent,  and  the 
embryology  can  follow  more  closely  the  ancestral 
history.  In  this  way  two  annelids  closely  related 
might  differ  radically  in  their  embryology,  without 
this  fact  at  all  affecting  the  truth  of  the  hypothesis 
that  embryology  tends  to  repeat  past  history. 

Or  take  a  still  more  striking  illustration.  Accord- 
ing to  modern  ideas  derived  from  anatomical  and 
paleontological  evidence,  the  ancestors  of  the  birds 
were  at  one  time  aquatic  animals,  breathing  by 
means  of  gills  somewhat  as  do  fishes.  If,  there- 
fore, embryology  repeated  exactly  the  past  history, 
we  should  expect  to  find  gills  in  the  embryo  chick. 
But  consider  the  condition  in  which  the  chick  passes 
its  embryonic  life:  closed  within  the  egg-shell,  un- 


EXPLAINING  THE   CONTRADICTIONS.  131 

able  to  move  to  any  great  extent,  and  certainly 
unable  to  breathe  by  means  of  gills,  and,  moreover, 
passing  through  its  entire  development  in  twenty- 
one  days.  Can  we  expect,  therefore,  that  even  if 
the  tendency  to  repeat  ancestral  forms  is  very 
strong,  there  will  be  time  and  opportunity  to  com- 
plete such  useless  structures  as  gills?  Now  the 
facts  are,  that  while  the  gills  themselves  have  dis- 
appeared, the  embryo  chick  does  possess  undoubted 
remains  of  them  in  two  features.  There  are  found 
in  the  embryo  openings  upon  the  sides  of  the  neck, 
which  mark  the  position  of  the  former  gill-slits ; 
and  the  blood-vessels  of  the  embryo  at  first  run  to 
these  slits  in  a  manner  which  shows  that  they  once 
supplied  gills  here  situated.  No  one  can  doubt 
that  here  are  the  homologues  of  a  former  aquatic 
respiratory  apparatus. 

This  case  is  then  most  readily  explained.  For,  if 
the  gills  are  of  no  use,  their  development  would  be 
of  positive  disadvantage.  Other  things  being  equal, 
it  is  desirable  that  the  embryo  should  go  through  its 
development  as  rapidly  as  possible,  since  the  species 
will  thus  multiply  more  rapidly,  and  also  because  it 
will  give  less  opportunity  for  the  destruction  of  the 
helpless  embryos  by  their  enemies.  The  chick  de- 
velops in  twenty-one  days,  and  it  is  therefore  prac- 
tically impossible  that  all  of  the  stages  of  its 
ancestral  history  can  be  exactly  repeated.  Much 
will  be,  of  necessity,  skipped,  much  faintly  sug- 
gested, and  the  whole  will  be  condensed  into  small 
compass.  Stages  of  fundamental  importance  will 
be  more  likely  to  be  retained  than  those  of  less 


132  EVOLUTION  OF  TO-DAY. 

moment.  We  can  then  readily  see  why  the  chick 
should  have  lost  its  gills  but  have  retained  the  gill- 
slits.  The  ancestral  stage  in  the  history  of  the 
chick  which  possessed  gills  occurred  very  long  ago  ; 
and  since  that  time  the  embryo  has  slowly  lost  the 
habit  of  developing  such  useless  structures.  If  it 
had  been  only  a  short  time  since  that  stage,  we 
might  still  expect  to  find  them.  This  we  do  find, 
for  instance,  in  a  frog  of  Guadaloupe,  which,  from 
the  absence  of  stagnant  water,  is  obliged  to  skip  the 
tadpole  stage,  or  rather  is  obliged  to  pass  through 
this  stage  before  hatching  from  the  egg.  In  this 
stage,  though  the  animal  is  still  in  the  egg,  there 
are  developed  gills  and  a  tail.  We  know  that  frogs 
are  a  recent  introduction  into  the  Guadaloupe,  and 
thus  see  that  it  takes  time  even  for  the  disappear- 
ance of  such  useless  organs  as  gills.  But  in  the  case 
of  the  chick  the  time  has  been  much  longer,  and 
every  trace  of  gills  has  disappeared.  We  might  ex- 
pect that  the  g\\\-slits  would  disappear  too  ;  but 
they  have  not;  they  still  remain  to  mark  the  former 
aquatic  life  of  the  ancient  vertebrates. 

If  a  shipbuilder  wishes  to  build  a  steamboat,  he 
moulds  his  material  directly  into  the  form  of  boat 
he  wishes  ;  we  would  think  little  of  his  ability  if  he 
began  by  building  a  canoe,  modified  this  into  a  row- 
ing boat,  this  into  a  Roman  trireme,  this  into  a 
simple  sailing  vessel,  this  into  a  large  ship,  and 
finally  into  a  steamboat.  Such  a  method  would 
be  repeating  the  history  of  the  steamship,  but 
would  be  a  poor  way  to  build  a  boat.  Now  the 
development  of  the  chick  is  a  compromise  between 


EXPLAINING  THE   CONTRADICTIONS.          133 

these  two  methods  of  direct  and  indirect  construc- 
tion. Instead  of  repeating  the  whole  past  history,  it 
attempts  in  some  features  to  build  the  chick  in  the 
most  direct  way,  and  drops  many  of  the  earlier 
stages.  But  it  has  not  succeeded  in  freeing  itself 
from  them  all,  the  tendency  to  reproduce  its  earlier 
history  being  strong  enough  to  preserve  many  of 
the  more  important  stages.  A  notochord  is  devel- 
oped which  represents  the  primitive  backbone  of 
the  vertebrates.  It  appears  in  the  young  chick,  but 
is  subsequently  completely  lost,  nothing  remaining 
in  the  adult  chick  to  indicate  its  existence.  The 
young  chick  develops  gill-slits  which  are  of  no.  use  to 
the  embryo  or  the  adult.  They  consequently  soon 
close  up  and  disappear,  with  one  exception,  which 
becomes  converted  into  an  entirely  different  struc- 
ture, the  Eustachian  tube  connecting  the  mouth 
with  the  inner  ear.  Blood-vessels  to  supply  these 
slits  also  appear,  but  having  no  use  now  that  respi- 
ration is  no  longer  carried  on  here,  soon  change 
their  position  and  come  to  supply  other  parts  of 
the  body.  In  these  respects  the  embryology  of  the 
chick  can  be  compared  to  the  building  of  a  steam- 
ship, where  the  builder  does  not  indeed  make  first  a 
Roman  trireme  complete,  but  goes  so  far  in  that 
direction  as  to  make  in  his  boat  the  long  tiers  of 
openings  for  oars.  Finding,  however,  after  he  gets 
his  steam-engine  into  the  boat,  that  oar-holes  are  no 
longer  of  any  use,  he  either  closes  them  up  or  con- 
verts them  into  port-holes.  Oars  he  never  makes, 
since  he  discovers  that  they  will  not  be  needed,  and 
to  make  them  would  be  sheer  loss  of  time. 


134  EVOLUTION  OF  TO-DAY. 

Let  us  not  lose  sight  of  the  problem  we  are  trying 
to  solve,  which  is  the  reason  for  the  contradictions 
found  in  the  embryological  histories  of  allied  animals. 
We  have  seen  some  of  the  causes  which  have  led  to 
the  modification  of  the  embryological  record,  and  it 
may  well  happen  that  two  allied  animals  may  be 
modified  in  different  degrees.  And  we  may  find 
some  cases  where  there  is  still  retained  what  is 
known  as  the  primitive  history,  i.  e.,  a  development 
which  so  far  as  we  can  judge  repeats  quite  exactly 
the  past  history.  Of  course  when  it  is  recognized 
that  the  embryological  record  can  be  modified,  there 
will  be  difficulty  in  deciding  just  what  the  primitive 
history  is.  If  it  is  admitted  that  the  record  can  be 
modified  in  some  respects,  what  right  can  there  be 
in  saying  that  any  given  history  is  unmodified  ? 
Naturalists  of  note  have  claimed  that  where  the 
falsification  of  the  record  is  once  admitted,  the  whole 
data  for  work  is  gone  ;  the  embryologist  has  used 
up  his  foundation  in  trying  to  build  his  structure. 
That  there  is  a  difficulty  here  no  one  will  deny  ; 
but  it  is  not  an  insurmountable  one.  Every  new 
fact  of  embryology  aids  in  the  solution  of  the  prob- 
lem, and  by  taking  all  of  the  facts  together  some 
general  rules  can  be  deduced  which  aid  in  solving 
the  difficulties  here  presented.  From  what  has 
been  already  said,  it  will  be  evident  that  in  embryos 
which  have  no  food  supplied  them  in  the  egg,  we 
may  expect  a  more  primitive  history  than  in  those 
cases  where  such  food  is  abundant.  Free  living 
embryos  we  might  expect  would  be  less  modified 
than  those  passing  their  development  in  the  body 


EXPLAINING  THE   CONTRADICTIONS.  135 

of  the  mother.  If  we  find  all  the  representatives  of 
a  large  group  agreeing  in  some  common  feature,  we 
may  usually  conclude  that  it  is  ancestral.  Organs 
of  no  use  to  the  embryo,  such  as  the  gills  of  the 
Guadaloupe  frog ;  organs  appearing  and  then  dis- 
appearing ;  organs  arising  and  being  subsequently 
converted  into  something  else,  may  all  be  unhesi- 
tatingly set  down  as  features  inherited  from  the 
past.  But  the  most  important  factor  in  enabling  us 
to  decide  in  any  given  case,  is  the  directness  or 
indirectness  of  the  development.  When  we  find 
that  the  young  is  built  in  a  straightforward  manner 
directly  from  the  egg,  we  may  rest  assured  that  the 
embryology  does  not  repeat  very  exactly  the  history 
of  the  past ;  but  when  the  formation  of  the  embryo 
takes  place,  by  means  of  a  long  series  of  round- 
about stages,  we  may  strongly  presume  that  some 
or  all  of  them  are  ancestral  stages.  An  absolutely 
direct  development  is  not  known,  for  every  animal 
passes  through  some  out-of-the-way  stages.  The 
development  of  the  chick  is  extremely  direct,  but 
even  here  many  ancestral  features  are  retained.  On 
the  other  hand,  no  animal  is  known  whose  embry- 
ology is  such  as  not  to  lead  us  to  believe  it  to  be 
abbreviated  in  some  respects.  But  at  the  same  time 
many  do  have  such  a  roundabout  history  as  to  in- 
dicate that  in  most  points  they  repeat  ancestral 
features.  When,  further,  it  is  found  that  those 
animals  with  a  direct  development  almost  universal- 
ly have  a  large  amount  of  food-yolk  in  the  egg,  and 
that  those  with  an  indirect  development  agree  in 
having  little  food,  and  are  consequently  not  able  to 


136  EVOLUTION  OF  TO-DAY. 

abbreviate  their  development  so  much,  the  question 
as  to  which  is  primitive  is  scarcely  doubtful.  And 
when,  finally,  it  is  seen  that  in  many  cases  it  can  be 
demonstrated  that  the  direct  development  is  simply 
a  much  abbreviated  form  of  the  indirect  development 
in  allied  animals,  no  doubt  can  remain  as  to  which 
is  the  primitive  history  representing  more  closely 
the  past  history  of  the  group.  It  becomes  evident 
that  the  falsification  of  the  record  does  not  prove 
an  insurmountable  barrier. 

The  Result  of  These  Considerations. 

By  various  suggestions,  then,  as  to  the  causes  for 
the  modification  of  the  embryology  under  certain 
circumstances  scientists  have  succeeded  in  explaining 
many  contradictions,  and  in  showing  why  it  is  that 
in  some  cases  the  history  of  animals  as  drawn  from 
embryology  is  not  parallel  with  that  drawn  from  the 
anatomical  relations  of  adults.  All  this  has  been 
done  without  in  the  least  detracting  from  the  force 
and  cogency  of  the  fundamental  assumption  that 
embryology,  when  rightly  understood,  is  a  resume 
of  past  history.  But  notice  the  position  that  is  now 
reached.  Instead  of  claiming  that  embryology 
is  always  a  safe  guide  in  interpreting  past  history  it 
is  acknowledged  that  it  seldom  gives  a  true  record, 
being  frequently  so  modified  that  a  large  portion  of 
the  history  is  lost  and  the  rest  much  disguised. 
Instead  of  proving  a  simple  subject  as  at  first 
promised,  embryology  has  grown  more  and  more 
complicated,  with  increasing  knowledge,  until  it  has 
almost  resolved  itself  into  the  attempt  to  distinguish 


RESULT  OF  THESE   CONSIDERATIONS.        137 

the  true  history  from  the  modified,  and  the  endeavor 
to  interpret  the  latter  by  means  of  the  former. 
But  in  spite  of  all  this,  or,  more  correctly,  because 
of  all  this,  the  belief  in  the  truth  of  the  hypothesis 
we  are  considering  has  grown  stronger  and  stronger. 
While  many  discrepancies  occur,  it  is  a  very  general 
rule  that  the  embryological  history  is  parallel  to 
that  which  we  hypothetically  draw  from  anatomical 
relations.  So  far  is  this  true,  that  we  can  predict  with 
great  exactness  the  course  of  development  of  any 
animal  if  we  know  its  relations.  And  the  facts  that  so 
many  cases  of  unmodified  history  are  known  and 
are  being  constantly  discovered,  which  not  only 
agree  with  each  other,  but  also  assist  in  intrepreting 
the  cases  of  modified  development ;  that  amid  this 
great  discord  there  is  after  all  an  underlying  har- 
mony, growing  more  and  more  apparent  with  every 
new  discovery ;  that  every  advance  in  knowledge 
tends  to  remove  some  of  the  difficulties  ;  and  that 
the  hypothesis  in  question  has  so  successfully  suc- 
ceeded in  overcoming  the  obstacles  in  its  way ; — all 
of  these  reasons  lead  embryologists  to  the  conclu- 
sion that  in  general  embryology  does  repeat  past 
history.  Indeed  they  have  long  since  ceased  to  dis- 
cuss the  question,  and  now  consider  it  wasted  time 
to  attempt  to  prove  it.  For  them  it  is  established. 
It  is  not  improbable  that  this  so  confident  belief 
may  be  partly  due  to  the  attitude  of  the  embryolo- 
gist  in  his  investigations.  He  is,  to  begin  with, 
fascinated  with  the  hypothesis,  and  naturally  tries 
to  explain  his  results  in  its  terms,  frequently  thus 
losing  sight  of  the  fact  that  one  of  the  chief  objects 


138  EVOLUTION  OF  TO-DAY. 

of  his  research  is  to  verify  it.  But  we  can  hardly 
believe  that  any  false  conclusion  will  be  long  enter- 
tained. The  naturalist  is  in  search  after  truth,  and 
must  at  all  events  be  considered  an  honest  man. 
Many  of  them  would  have  been  glad  to  disprove 
this  hypothesis  if  it  had  been  possible.  When, 
therefore,  all  embryologists,  who  are  the  only  ones 
who  can  rightly  interpret  the  evidence,  are  agreed 
that,  in  spite  of  the  complications  arising  from  the 
falsification  of  the  embryological  record,  the  three 
series  of  historical  lines  obtained  from  paleontology, 
classification,  and  embryology,  are  parallel,  the  can- 
did mind  must  accept  this  verdict  as  one  of  the 
well-attested  facts  of  science.  But  it  is  a  fact  which 
cannot  from  the  very  nature  of  the  case  be  proved. 

Rmbryology  as  an  Assistance  in  Classifying  Animals. 

The  extent  to  which  this  idea  of  embryology  and 
descent  has  forced  its  way  into  science,  is  indicated 
by  the  modern  method  of  classifying  animals. 
Early  in  the  century  Von  Baer  first  proved  that  the 
development  of  the  individuals  of  the  various  groups 
of  animals  was  such  that,  as  he  says,  the  different 
types  have  different  types  of  development.  Since 
his  time  this  conclusion  has  been  subjected  to  rigid 
examination  in  every  direction,  with  the  general 
result  of  confirming  it,  except  in  the  earliest  stages. 
But  this  confirmation  has  been  by  no  means  such  as 
Von  Baer  expected.  Instead  of  leading  to  the  es- 
tablishment of  types,  it  has  broken  them  to  pieces, 
and  has  disclosed  not  four,  but  over  twenty  types  of 
development.  The  true  result  is  that  animals  closely 


EMBRYOLOGY  IN  CLASSIFYING  ANIMALS.    139 

related  agree  in  their  development ;  that  species 
which  form  a  circumscribed  group  usually  have  a 
circumscribed  type  of  development.  The  embry- 
ologist  can  predict  with  almost  certainty  exactly 
what  the  development  of  any  animal  will  be,  if  he 
knows  its  adult  relationship.  So  close  is  this  par- 
alleled, that  scientists  have  considered  themselves 
justified  in  reversing  the  argument  and  in  basing 
their  classifications  upon  embryology.  Almost  all 
of  the  advances  made  in  the  classification  of  the 
larger  groups  are  made  through  the  study  of  embry- 
ology ;  no  classification  is  considered  complete  with- 
out it;  and  in  many  points,  indeed,  the  conclusions 
as  to  relationship  are  based  on  this  study  alone. 
And  this  fact  is  conclusive  evidence  that  continued 
investigations  show,  in  spite  of  the  numerous  con- 
tradictions, a  parallelism  between  embryology  and 
that  hypothetical  history  which  we  should  build 
from  the  study  of  adults.  Von  Baer  certainly  dis- 
covered an  important  principle,  although  it  no 
longer  stands  as  he  formulated  it.  To-day  it  reads 
something  as  follows:  Closely  related  animals  agree 
in  their  development,  while  those  distantly  related 
show  no  likeness  except  in  the  early  stages ;  but 
since  all  of  the  members  of  the  large  groups  of  ani- 
mals have  had  in  the  past  a  common  history,  it  will 
follow  that  they  will  have  a  common  embryology,  if 
one  is  the  repetition  of  the  other.  We  thus  explain 
the  fact  that  the  so-called  types  of  animals  have 
their  own  types  of  development. 

We  may,  then,  safely  assert  that  the  investiga- 
tions have  strengthened  almost  to  proof  the  funda- 


140  EVOLUTION  OF  TO-DAY. 

mental  law  of  embryology,  that  the  development  of 
the  individual  is  a  repetition  of  past  history.  It  is 
supported  by  the  comparison  of  embryology  with 
paleontology,  by  the  complete  harmony  amid  the 
*"  discord  coming  from  its  comparison  with  the  hypo- 
thetical history  which  classification  teaches,  and  by 
the  fact  that  it  not  only  enables  the  student  to  ex- 
plain difficulties,  but  also  to  make  predictions — the 
best  test  of  any  scientific  theory.  Considering  it, 
therefore,  as  practically  demonstrated,  we  proceed 
to  the  consideration  of  its  meaning. 

2. —  The  Significance  of  the  Parallel  between  Embry- 
and  Past  History. 


The  real  question  as  to  whether  embryology  forms 
an  argument  for  evolution,  concerns  the  explanation 
we  can  give  to  the  parallel  which  has  been  under 
consideration.  The  embryologist  assumes  that  the 
parallelism  proves  evolution,  and  busies  himself  in 
studying  details  and  constructing  from  the  evidence 
as  correctly  as  possible  the  genealogical  history  of 
animals.  Before  following  him  into  this  field,  we 
must  first  take  a  more  general  view  of  the  matter 
and  discover  the  true  significance  of  the  principles 
on  which  he  works. 

In  reality  the  teachings  of  embryology,  as  ex- 
pounded by  its  students  and  as  verified  by  modern 
research,  form  the  strongest  direct  argument  in 
favor  of  the  theory  of  descent.  The  parallel  in 
question  is  certainly  one  of  the  most  marvellous  dis- 
coveries ever  made  ;  a  discovery  which  would  never 
have  been  dreamed  of  from  a  priori  grounds.  Why 


EMBRYOLOGY  AND  PAST  HISTORY.  14! 

should  an  embryo  go  over  such  a  roundabout  road 
in  development,  instead  of  proceeding  to  the  adult 
in  the  most  direct  manner?  If  possible  an  explana- 
tion must  be  given  ;  and  if  an  explanation  can  be 
given  in  accordance  with  natural  law,  it  is  far  prefer- 
able to  do  so  than  to  leave  the  whole  matter  in  the 
realm  of  the  supernatural.  Now  the  theory  of  evo- 
lution has,  or  rather  M,  an  explanation  of  this  paral- 
lel. It  is  not  yet,  perhaps,  from  the  want  of  knowl- 
edge, perfectly  satisfactory  in  every  point.  But  it  is, 
on  the  whole,  so  intelligible,  its  obscure  points  are 
so  rapidly  being  removed,  and  it  so  admirably  fits 
all  the  facts,  that  it  seems  hardly  possible  that  it 
is  not  the  true  explanation.  We  know  that  animals 
begin  their  development  as  a  single-celled  ovum  ; 
and,  according  to  the  descent  theory,  a  single-celled 
animal  was  a  stage  very  near  the  starting-point  of 
life  in  the  past  ages.  We  know  that  animals  do  in- 
herit the  characteristics  of  their  ancestors ;  not  only 
those  of  their  parents,  but  of  more  remote  genera- 
tions. There  is  abundance  of  evidence  for  the  fact 
that  these  inherited  characteristics  may  be  developed 
in  the  offspring  at  an  earlier  period  than  they  appear 
in  the  parent,  and  thus  peculiarities  of  the  adult 
may  slowly  become  those  of  younger  stages.  Now, 
with  all  of  these  facts  in  mind,  it  is  very  easy  to  see 
why  it  is  that  in  developing  from  the  single-celled 
ovum  to  the  adult,  the  embryo  should,  by  the  ac- 
cepted law  of  heredity,  pass  over  the  same  road 
which  was  travelled  by  its  ancestors  in  developing 
from  the  unicellular  animal  to  its  present  condition. 
Heredity,  then,  that  mysterious  law  which  we  know 


142  EVOLUTION  OF  TO-DAY. 

as  a  fact  but  do  not  understand,  is  an  explanation 
of  this  parallel.  With  this  principle  we  can  under- 
stand why  it  is  that  the  embryos  of  higher  animals 
resemble  the  adult  stages  of  lower  ones,  and  re- 
semble also  the  animals  of  geological  times;  we 
see  why  it  is  that  embryology  is  always  an  attempt 
at  a  repetition  of  past  history,  and  also  why  it  is 
that,  owing  to  surrounding  conditions,  the  attempt 
is  not  always  successful.  It  has  been  the  work  of 
the  last  twenty  years  of  embryology  to  show  that 
this  explanation  is  satisfactory,  and  that  it  throws 
light  upon  the  whole  subject  of  animal  life.  Al- 
though, as  we  shall  presently  see,  many  questions 
still  remain  for  solution,  enough  has  been  done  to 
show  that  the  result  will  eventually  be  a  harmony. 

This  is  the  simplest  explanation  for  the  fact 
offered,  but  it  is  not  a  conclusion  that  cannot  be 
gainsaid.  Many  people  have  fully  recognized  the 
parallel  in  question  and  yet  denied  evolution.  Just 
as  it  is  possible  to  claim  that,  while  the  facts  of 
paleontology  are  such  as  would  follow  from  the 
theory  of  evolution,  they  simply  prove  that  animals 
of  higher  and  higher  organization  have  appeared  in 
successive  ages,  and  do  not  prove  genetic  descent ; 
just  as  it  is  possible  to  claim  that,  while  all  of  the 
facts  of  classification  and  homology  receive  their 
most  simple  explanation  from  the  descent  theory, 
yet  they  do  not  prove  it :  so  here  it  is  possible  to 
contend  that  this  remarkable  fact  is  only  a  part  of 
a  preconceived  harmony — a  proof  of  the  unity  of 
the  organic  world.  And  for  this  unity  we  have  seen 
that  the  theory  of  types  offers  its  explanation.  The 


EMBRYOLOGY  AND  PAST  HISTORY.  143 

argument  from  embryology  is,  therefore,  similar 
in  its  nature  to  that  which  has  been  found  in  classi- 
fication and  paleontology,  but  it  is  at  the  same  time 
a  more  forcible  argument.  It  is  much  easier  to 
understand  that  even  on  the  theory  of  special  crea- 
tion of  species,  animals  should  have  appeared  in  the 
order  we  have  discovered,  and  should  be  related  to 
each  other  according  to  a  tree-like  schema,  than  to 
understand  why  the  embryo  should  go  so  much  out 
of  its  way  to  repeat  stages  which  have  never  been 
comprised  in  the  history  of  its  own  ancestry. 

It  is  hardly  necessary  to  do  more  than  state  this 
argument,  for  its  force  is  one  that  each  individual 
must  settle  in  his  own  mind.  The  facts  are  as 
stated,  the  conclusion  from  them  each  must  de- 
termine for  himself.  The  teachings  of  embryology, 
since  the  appearance  of  the  "  Origin  of  Species," 
have  been  found  to  be  in  harmony  with  the  descent 
theory  ;  its  very  contradictions,  when  rightly  under- 
stood, forming  the  strongest  confirmation  of  the 
fact.  The  embryologist,  finding  how  perfectly  the 
facts  harmonize,  is  simply  unable  to  avoid  the  con- 
clusion that  the  fact  of  an  animal  being  embryologi- 
cally  derived  from  an  older  form,  is  proof  that  his- 
torically the  same  descent  is  true.  He  is  unable  to 
avoid  the  use  of  the  term  relationship,  or  to  avoid 
interpreting  the  word  as  meaning  ^^-relationship. 
And  so  the  matter  stands  to-day.  That  the  develop- 
ment of  the  individual  repeats  the  development  of 
the  race,  is  a  fact  abundantly  demonstrated.  The 
theory  of  evolution  offers  the  only  natural  solution 
of  the  fact,  an  explanation  which,  when  thoroughly 


144  EVOLUTION  OF  TO-DAY. 

applied,  is  found  to  fit  the  facts  marvellously  welL 
"  On  the  hypothesis  of  evolution  this  parallelism 
has  a  meaning — indicates  that  primordial  kinship  of 
all  organisms  and  that  progressive  differentiation  of 
them  which  the  hypothesis  alleges.  But  on  any 
other  theory  the  parallelism  is  meaningless,  or, 
rather,  it  raises  a  difficulty,  since  it  implies  either  an 
effect  without  a  cause,  or  a  design  without  a  purpose." 

Difficulties  to  be  Overcome. 

The  task  of  discovering  the  history  of  animals, 
even  when  we  have  the  key  to  the  problem  in  their 
development,  is  by  no  means  an  easy  one.  In  the 
first  place,  difficulties  of  observation  have  proved 
very  great.  Hardly  two  animals  can  be  studied  in 
the  same  way,  and  it  has  severely  exercised  the  in- 
genuity of  our  scientists  to  discover  how  single  indi- 
viduals can  be  studied.  But  this  difficulty  has  been 
gradually  disappearing.  A  second  complication  is 
more  serious.  From  the  difficulty  of  observation  it 
has  resulted  that  few  of  the  observations  of  twenty- 
five  years  ago  can  be  relied  upon.  The  older  em- 
bryologists  did  not  realize  how  very  easy  it  is  to 
make  mistakes  in  their  observations  on  such  minute 
organisms.  A  little  whirling  embryo,  only  semi- 
transparent,  is  a  very  difficult  object  to  study,  even 
with  the  best  methods  and  conveniences.  It  is 
therefore  to  be  expected  that  the  first  observations, 
made  with  imperfect  instruments,  should  be  very 
faulty.  And,  moreover,  the  simplest  principles  of 
the  subject  were  then  unknown,  and,  with  nothing 
for  a  guide,  the  early  observers  did  not  even  know 


DIFFICULTIES  TO  BE   OVERCOME.  145 

what  to  look  for,  and  in  a  subject  as  difficult  for  ob- 
servation as  this,  it  is  almost  necessary  to  know  what 
to  expect.  In  short,  all  of  the  errors  belonging  to 
the  infancy  of  a  subject  are  found  in  the  older  in- 
vestigations, and  it  has  been  necessary,  therefore,  to 
make  numerous  corrections.  They  are  constantly 
being  made,  and  with  a  new  understanding  of  what 
is  significant  and  what  unimportant,  new  interpre- 
tations are  being  gained.  From  the  general  uncer- 
tainty in  regard  to  former  work,  it  is  necessary  now 
to  review  almost  everything  which  was  done  earlier 
than  twenty-five  years  ago,  if  one  wishes  to  make 
sure  of  any  important  point.  The  modern  student 
has  found  that,  so  far  as  superficial  observations 
were  concerned,  the  older  embryologists  were  accu- 
rate and  painstaking  in  what  they  saw,  but  the 
internal  anatomy,  and  particularly  the  changes 
which  take  place  in  various  stages,  they  were  likely 
to  describe  incorrectly. 

Further  difficulty  has  arisen  out  of  the  fact,  al- 
ready dealt  with  at  some  length,  that  the  embryo- 
logical  history  is  so  frequently  modified.  Not  only 
has  food-yolk  produced  a  series  of  modifications, 
but  another  entirely  different  sort  of  changes  has 
arisen  in  free  larvae.  Many  animals  pass  part  of 
their  early  development  as  free-living,  independent 
organisms,  as  independent,  indeed,  as  the  adults. 
The  caterpillar  is  nothing  more  than  an  embryonic 
stage  of  the  butterfly,  and  is  sometimes  more  inde- 
pendent than  the  butterfly  itself.  Such  larvae,  living 
as  free  forms,  obtain  their  food  by  their  own  exer- 
tions, and  have  many  enemies  to  contend  with. 


146  EVOLUTION  OF  TO-DAY. 

They  are,  therefore,  as  truly  engaged  in  a  struggle 
for  existence  as  the  adult.  Now,  since  these  larvae 
are  known  to  be  subject  to  variation,  there  is  no 
reason  why  the  action  of  the  environment  should 
not  modify  them  as  much  as  it  does  the  perfectly- 
developed  insect.  If  this  occurs,  the  larvae  immedi- 
ately begin  to  depart  from  the  typical  form,  and  the 
embryological  history  is  much  modified.  Abundant 
instances  of  this  occur  in  Echinoderms,  Crustacea, 
and  insects.  We  see,  therefore,  that  the  embryologist 
has  to  deal  with  modifications  arising  from  a  station- 
ary, dependent  condition  of  the  embryo,  and  others 
arising  from  its  free,  independent  existence.  Neither 
the  direct  nor  indirect  development  can  be  implicitly 
relied  upon.  It  would  almost  seem,  therefore,  that 
here  was  a  bar  to  further  advance.  Some  biologists 
have  expressed  themselves  as  out  of  sympathy  with 
any  further  reasoning  after  the  great  falsification  of 
the  record  is  once  admitted.  But  the  difficulty  is 
not  so  great  as  it  seems.  Undoubtedly,  such  modi- 
fications exist,  and  the  only  question  is  as  to  the 
ability  of  the  student,  with  the  evidence  at  his  com- 
mand, to  recognize  them.  Of  course,  this  cannot 
be  done  from  single  specimens,  but  it  has  been 
found  possible  in  many  cases,  by  the  collection  of 
great  masses  of  data,  to  straighten  effectually  the 
evidence  and  get  some  logical  results.  But  it  is 
certainly  necessary  to  withhold  any  conclusions 
until  we  can  get  all  of  the  evidence  possible  from 
every  source,  in  expectation  that  when  all  comes  to 
be  considered  together  the  truth  may  be  plainly 
apparent.  The  wiser  embryologists,  therefore,  have 


THE  APPLICATION  OF  THIS  PRINCIPLE,      147 

postponed  formulating  any  more  histories  of  ani- 
mals, until  such  time  as  the  abundance  of  evidence 
shall  enable  them  to  reach  more  legitimate  conclu- 
sions. In  short,  although  embryology  is  believed  to 
be  a  key  to  animal  history,  it  proves  so  difficult  to 
use  that  many  doors  still  remain  locked. 

The  Application  of  this  Principle, 

Having  recognized  the  parallel,  and  having  con- 
sidered its  significance,  we  have  stated  the  whole  of 
the  direct  argument  which  embryology  has  to  offer. 
It  is  impossible,  however,  to  get  a  correct  idea  of  the 
real  force  of  the  argument  without  examining  some 
of  the  results  of  the  application  of  the  principle. 
We  will  now,  therefore,  proceed  to  consider  what 
embryology  has  taught  us  of  the  history  of  animals. 

All  embryological  discussion  is  now  based  on  the 
tacitly  understood  assumption,  that  an  animal's  de- 
velopment is  a  repetition  of  the  history  of  its  ances- 
tors, and  that  a  complete  knowledge  of  the  former 
would  give  us  an  approximately  perfect  knowledge 
of  the  latter.  By  a  complete  knowledge  of  develop- 
ment is  not  meant  simply  the  knowledge  of  the 
present  actual  course  of  embryonic  growth,  for 
when  the  possibility  of  the  modification  of  the 
record  is  recognized,  it  becomes  plain  that  the 
knowledge  of  the  actual  embryology  is  by  no  means 
a  complete  understanding  of  its  development.  A 
complete  knowledge  would  imply  a  knowledge  of 
the  primitive  type  of  development,  and  the  method 
by  which  the  modified  type  has  been  derived,  to- 
gether with  the  circumstances  accompanying  the 


148  EVOLUTION  OF  TO-DAY. 

change.  Such  a  complete  knowledge  as  this  it  is 
useless  to  hope  for,  but  every  day  gives  a  closer  ap- 
proximation to  it,  and  it  is  quite  probable  that  the 
state  of  the  science  may  reach  a  condition  where  it  will 
be  possible  to  sketch  the  general  history  of  animals. 
A  short  summary  of  the  teachings  of  embryology 
is  something  as  follows :  All  animals  start  together 
as  a  single  cell,  so  that  the  man  cannot  be  distin- 
guished from  the  lobster  or  mollusk.  An  embryo 
arises  from  this  cell,  which  shows  itself  to  be  a  ver- 
tebrate in  distinction  from  an  invertebrate,  but  is  as 
yet  not  a  mammal,  but  more  like  a  fish.  With  further 
development  it  shows  a  slight  approximation  toward 
the  reptiles,  but  instead  of  becoming  a  member  of 
this  class,  takes  a  little  different  course  and  declares 
itself  to  be  a  mammal.  Next,  it  turns  toward  the 
direction  of  the  primates  rather  than  rodents  or 
ungulates ;  then  it  exhibits  the  characteristics  of  an 
ape,  in  distinction  from  the  Lemurs  ;  and  finally, 
just  before  birth,  it  takes  on  the  features  of  man. 
And  this  same  story  is  repeated  in  all  cases,  the  line 
of  development  being  the  sub-kingdom,  the  class, 
the  sub-class,  the  order,  the  family,  the  genus,  the 
species,  thus  coinciding  with  one  tree-like  classifi- 
cation of  animals.  While  this  is  the  general  history, 
some  points  demand  more  extended  notice. 

The  Abundance  of  Hypothetical  Stages. 

Considering  all  of  these  difficulties,  we  are  pre- 
pared to  be  somewhat  disappointed  when  we  try  to 
take  a  general  view  of  the  positive  results.  The 
positive  conclusions  are  few,  the  negative  conclusions 


ABUNDANCE   OF  HYPOTHETICAL   STAGES.    149 

are  many.  The  embryologist  does  not  seem  to  know 
so  much  about  the  history  of  animals  as  he  did 
twenty  years  ago.  In  reality  the  reverse  of  this  is 
the  truth,  for  these  twenty  years  have  seen  a  con- 
tinual advance.  While  they  have  disproved  many  of 
the  old  views,  they  have  taught  the  student  to  be 
cautious  in  founding  conclusions  on  insufficient  data. 
In  the  very  infancy  of  the  subject,  Haeckel  boldly 
traced  the  complete  history  of  man  from  the  simple 
protozoan  to  his  present  condition.  Without  hesi- 
tation he  laid  down  the  complete  genealogy  of  man 
from  evidence  found  in  his  development,  with  no 
attempt  to  get  help  from  other  sources.  And  in- 
asmuch as  embryology  was  in  a  very  crude  con- 
dition at  that  time,  we  are  not  surprised  to  find 
that  this  genealogy  contained  more  errors  than 
truths.  He  divided  man's  history  since  the  ap- 
pearance of  life  into  twenty-one  stages,  which  he 
thought  were  indicated  by  stages  in  his  develop- 
ment. It  is  needless  here  to  enumerate  these 
stages,  for  little  by  little  has  it  become  evident  that 
most  of  them  were  guesses,  or  at  least  founded  on 
very  insufficient  data.  Of  these  twenty-one  stages, 
more  than  half  have  been  proved  to  be  wrong,  and 
in  regard  to  some  of  the  others  it  is  questionable. 
This  attempt  of  Haeckel,  made  with  such  boldness 
as  almost  to  inspire  belief,  is  thus  a  failure.  Nor  has 
Haeckel  been  alone  in  this  attempt,  for  others  have 
essayed  a  like  task.  Darwin,  with  all  his  caution, 
was  led  in  his  "  Descent  of  Man  "  to  trace  out  his 
history,  and  he  came  no  nearer  the  truth  than  did 
Haeckel.  But  to-day  the  wiser  naturalists  do  not 


1 50  E  VOL  UTION  OF  TO-DA  Y. 

pretend  to  know  so  much  about  the  matter,  and 
although  they  do  occasionally  construct  similar  his- 
tories, they  regard  them  only  as  tentative,  and 
probably  erroneous  in  many  features.  They  have 
disproved  Haeckel's  phylum,  but  have  put  nothing 
;  in  its  place.  They  are  not  ready  to  say  exactly 
what  man's  genealogy  has  been,  but  can  say  very 
definitely  what  it  has  not  been,  a  conclusion  whicli, 
though  not  appealing  so  strongly  to  the  imagination, 
is  a  much  more  important  one. 

But  this  conclusion  is  more  than  a  negative  result, 
for  its  existence  leads  to  one  very  definite  and 
important  deduction — perhaps  the  most  important 
one  which  embryology  has  brought  into  prominence. 
Stated  briefly  it  is  this:  Probably  none  of  the 
stages  through  which  man,  or  any  other  existing 
animal,  has  passed  in  his  history,  exist  as  living  ani- 
mals to-day.  This  point  has  been  emphasized 
repeatedly.  The  parallel  often  drawn  between  the 
embryonic  stages  of  higher  animals  and  the  adult 
stages  of  lower  ones,  proves  upon  close  examination 
to  be  largely  a  delusion.  The  embryonic  stages  of 
higher  animals  resemble  not  the  adult  stages  but 
the  embryonic  stages  of  lower  animals.  Embryo 
man,  for  instance,  does  not  resemble  the  monkey, 
but  at  one  stage  in  their  development  the  embryos  of 
these  two  species  scarcely  differ  from  each  other. 
The  human  embryo  does  not  resemble  a  fish,  but 
both  man  and  the  fish  pass  through  a  stage  in  which 
they  are  much  alike.  Now  the  interpretation  of 
these  facts  means  simply  this.  Man  is  not  descend- 
ed from  any  of  the  man-like  apes,  but  both  man  and 


ABUNDANCE   OF  HYPOTHETICAL   STAGES.    151 

ape  are  descended  from  a  third  form  not  living  to- 
day, but  which  is  represented  by  the  stage  which 
the  two  embryos  have  in  common  just  before  birth. 
Now  this  hypothetical  form  was  neither  man  nor 
monkey,  but  midway  between  them.  If  we  should 
find  his  bones  in  the  rocks  we  might  not  unlikely 
call  him  an  ape,  but  if  we  should  know  more  about 
him  we  should  find  that  he  did  not  resemble  any 
animal  living  to-day.  Or  again,  man  has  not  descend- 
ed from  an  animal  like  our  modern  fish,  but  both 
man  and  our  fishes  have  descended  from  a  third 
intermediate  form.  This  form  doubtless  lived  in 
the  water  and  would  probably  be  called  a  fish  were 
we  to  discover  its  remains  in  the  rocks,  but  it  was  in 
reality  very  different  from  our  modern  fishes.  For 
a  time  our  fishes  and  mammals  travelled  together, 
but  soon  one  group  took  one  direction  and  the 
other  another,  both  continuing  to  develop,  getting 
farther  and  farther  from  each  other  and  from  this 
common  ancestor.  And  so  everywhere.  The  types 
of  animals  which  were  the  common  ancestors  of  our 
existing  groups  are  all  extinct.  Embryology  shows 
us  that  if  we  wish  to  trace  the  past  history  of  ani- 
mals, it  must  be  mostly  done  through  hypothetical 
forms,  which  have  existed  in  the  past  but  are  now 
extinct. 

The  extent  to  which  this  principle  is  true,  is  excel- 
lently illustrated  by  a  tentative  ancestry  of  the 
vertebrates  as  taught  by  one  of  the  ablest  of  modern 
scientists.  If  one  takes  the  trouble  to  refer  to  vol.  ii. 
of  Balfour's  "Comparative  Embryology,"  it  will  be 
seen  that  he  derives  the  mammals  from  the  earliest 


152  EVOLUTION  OF  TO-DAY. 

vertebrates  by  six  stages,  every  one  of  which  he 
acknowledges  to  be  hypothetical. 

Here,  again,  it  would  seem  that  embryologists  had 
abandoned  a  definite  position  for  an  indefinite 
one ;  but  a  little  thought  will  show  that  this  latter 
position  is  the  true  one.  If  evolution  is  true,  ani- 
mals are  continually  changing,  either  slowly  or  by 
occasional  rapid  advances,  and  that  any  single  form 
should  retain  its  specific  characters  for  a  great  (geo- 
logically speaking)  length  of  time,  would  be  the  ex- 
ception and  not  the  rule.  These  hypothetical  stages 
which  we  are  considering  must  have  disappeared 
very  long  ago.  To  be  sure,  as  already  pointed  out, 
time  does  not  necessarily  imply  change,  but  in  these 
cases  we  know  the  change  has  taken  place.  The 
very  fact  that  the  ancestor  of  man  became  modified 
in  two  directions,  one  toward  man  and  the  other 
toward  the  monkey,  would  preclude  us  from  finding 
any  representative  of  this  ancestor  living.  Connect- 
ing links  will,  therefore,  almost  always  disappear. 
Although  living  links  between  different  groups  are 
occasionally  found,  it  is  hardly  probable  that  they 
represent  the  true  ancestral  forms.  The  demand 
for  the  "  missing  link,"  once  considered  so  great  an 
argument  against  evolution,  ceases  to  be  of  any 
significance  with  this  understanding. 

But,  nevertheless,  granting  all  of  this,  it  is  evident 
that  these  hypothetical  ancestors  must  have  existed 
at  one  time,  if  the  descent  theory  be  true.  Have 
they  left  no  trace?  If  we  can  find  no  living  repre- 
sentatives of  them,  we  certainly  ought  to  find  them 
represented  by  fossils.  We  are  thus  brought  back 


ABUNDANCE   OF  HYPOTHETICAL   STAGES.    153 

once  more  to  the  subject  of  paleontology,  into  which 
we  need  not  again  enter.  To  a  certain  extent, 
naturalists  have  succeeded  in  finding  among  fossils 
remains  of  animals  which  may  well  be  these  hypo- 
thetical forms,  but  it  must  be  confessed  that  their 
success  has  not  been  very  great.  Aside  from  the 
general  imperfection  of  the  geological  record,  several 
distinct  reasons  can  be  given  for  this.  Firstly, 
most  of  these  stages,  concerning  which  embryology 
teaches  us,  must  have  lived  far  back,  in  ages 
which  have  left  few  fossils.  But,  secondly,  we  notice 
that  embryology  can  give  us  only  the  general  char- 
acteristics of  these  forms,  and  says  not  a  word  as  to 
their  specific  features.  Now,  every  fossil  must  have 
specific  as  well  as  general  features,  and  the  presence 
of  the  former,  which  are  often  more  prominent,  may 
obscure  the  latter.  Thirdly,  all  of  these  stages 
would  resemble,  more  or  less,  one  of  the  groups 
which  they  connect.  If  our  paleontologist  should, 
therefore,  find  an  imperfect  representative  of  such 
a  connecting  link,  he  would  usually  class  it  with  one 
or  the  other  group,  without  recognizing  its  imme- 
diate character.  It  is  not  improbable  that  the  fish- 
scales  found  in  the  Silurian  age  belonged  to  one  of 
the  very  hypothetical  stages  of  which  embryology 
teaches,  but  how  are  we  to  know  whether  it  be  so 
or  not?  These  scales  come  nearer  to  those  of  a  fish 
than  to  any  thing  else  we  know,  and  they  are  there- 
fore said  to  belong  to  a  fish.  The  absence  of  these 
hypothetical  stages  is,  therefore,  not  very  surprising, 
though  it  is  certainly  unfortunate. 


154  EVOLUTION'  OF  TO-DAY. 

Embryological  History. 

Having  now  noticed  these  various  difficulties  in 
the  way  of  a  complete  history,  let  us  begin  with 
early  stages  of  development  and  see  how  far  any 
logical  history  can  be  traced.  Of  the  early  stages 
of  development  embryologists  have  made  us  well 
acquainted,  for  they  have  spent  most  of  their  time 
on  this  subject.  Owing  to  the  difficulties  of  observa- 
tion upon  older  embryos,  it  is  the  early  stages  which 
have  received  most  attention.  But  this  necessity 
has  not  been  an  unfortunate  one.  It  is  evident, 
from  the  fact  that  all  of  the  great  groups  of  animals 
were  already  developed  in  the  earliest  rocks,  that 
paleontology  can  tell  us  nothing  in  regard  to  the 
development  of  these  groups,  and  their  relation  to 
each  other ;  a  fact  which  has  been  used  as  an  argu- 
ment for  the  primitive  distinction  of  types.  Now, 
embryology  comes  in  to  fill  up  this  lost  history. 
The  early  stages  of  the  embryo  must,  of  course, 
represent  the  first  stages  of  this  lost  record,  and 
ought  to  give  the  relation  of  the  sub-kingdoms  to 
each  other.  The  later  stages  represent  later  history 
and  the  origin  of  smaller  groups.  The  latest  stages 
will  represent  the  growth  of  the  smaller  groups  of 
genera.  Now,  the  study  of  classification  gives  good 
evidence  as  to  the  origin  of  small  groups;  paleon- 
tology enables  us  to  trace  the  history  of  the  origin 
of  orders,  etc. ;  but  embryology  alone  can  give  us 
evidence  as  to  the  relation  of  the  sub-kingdoms  to 
each  other.  It  is,  then,  a  fortunate  necessity  which 
has  led  to  a  particularly  careful  study  of  early  stages 
of  the  embryos  of  a  very  large  number  of  animals; 


EMBRYOLOGICAL  HISTORY.  155 

for  no  other  branch  of  science  is  able  to  lead  to  any 
conclusions  as  to  the  union  of  the  great  branches  of 
the  animal  kingdom  into  a  common  trunk. 

All  animals  start  together.  At  the  beginning  of 
life  the  highest  and  lowest  alike  consists  of  a  simple 
single-celled  ovum.  This  is  the  universally  recog- 
nized starting-point.  Interpreting  this,  therefore, 
the  embryologist  says  that  it  means  that  we  are  to 
assume  as  the  starting-point  of  life  of  the  animal 
kingdom  a  single-celled  ancestor,  or  protozoan,  who 
lived  long  before  the  earliest  record  which  the  rocks 
give  us.  Next,  we  find  that  this  ovum  divides  into 
a  number  of  smaller  parts,  each  consisting  of  a  single 
cell,  and  all  at  first  seemingly  alike,  cases  where  they 
are  unlike  being  due  to  secondary  modifying  circum- 
stances. This  is  called  segmentation,  and  is  a  stage 
in  development  universally  found  in  all  animals.  It 
is  not  alike  in  all,  for  the  disturbing  presence  of  food 
in  the  egg  often  prevents  a  regular  division.  Some- 
times the  whole  ovum  divides,  sometimes  part  of  it ; 
sometimes  the  segments  are  of  equal  size,  sometimes 
of  different  sizes.  But  after  a  careful  examination 
of  all  cases  and  circumstances  connected  with  them, 
the  conclusion  seems  to  be  that  they  are  all  modifi- 
cations of  the  simplest  type,  and  the  regular  equal 
division  may  be  considered  as  primitive.  Now,  this 
division  can  mean  but  one  thing  to  the  embryolo- 
gist. It  is  the  repetition  of  a  similar  process  taking 
place  long  ago  in  the  primitive  unicellular  ancestor 
of  animals,  which  is  supposed  to  have  divided  in 
like  manner,  and  thus  to  have  formed  a  colony  of 
unicellular  animals.  This  same  process  is  known  to 
take  place  to-day  in  some  low  forms  of  life. 


156  EVOLUTION  OF  TO-DAY. 

We  can  take  yet  another  step  in  the  development 
and  still  find  all  animals  to  agree.  We  reach  thus 
the  much-discussed  gastrula  stage.  In  its  simplest 
form  the  gastrula  is  a  two-layered  sac,  open  at  one 
end.  The  two  layers  of  the  sac  are  composed  of  the 
small  cells  into  which  the  ovum  has  divided.  These 
two  layers  are  different  from  each  other,  for  the 
outer  one  is  the  body-wall,  and  is  sensitive,  while  the 
inner  one  corresponds  to  the  digestive  tract.  The 
opening  of  the  sac  is  the  mouth,  and  is  believed  to 
correspond,  partially  at  least,  to  the  mouth  of  higher 
animals. 

According  to  Haeckel,  this  gastrula  is  a  universal 
stage  of  development,  and  represents  the  common 
ancestor  of  all  animals.  There  has  hardly  been  in 
the  history  of  science  a  more  happy  prediction, 
founded  on  such  insufficient  data,  as  this  gastrea 
theory  of  Haeckel.  At  the  time  it  was  made,  em- 
bryology was  a  very  young  science,  but  compara- 
tively few  facts  were  known,  and  many  of  the  then 
accepted  facts  have  since  proved  to  be  erroneous. 
But  Haeckel,  finding  that  many  animals  which  he 
had  been  fortunate  enough  to  study  passed  through 
a  stage  resembling  a  two-layered  sac,  with  his  char- 
acteristic boldness  he  made  the  prediction  that  this 
stage  would  be  found  universal  in  the  animal  king- 
dom, and  concluded  that  it  consequently  represented 
an  animal,  living  in  ages  past,  which  was  the  com- 
mon ancestor  of  the  whole  animal  kingdom.  And 
it  is  marvellous  how  this  prediction  has  little  by  little 
been  shown  to  be  at  least  partially  true.  Taking  a 
survey  of  the  whole  field  of  embryology  to-day,  it  is 


EMBRYOLOGICAL  HISTORY.  157 

a  fair  statement  to  say  that  there  is  not  a  group  of 
animals,  with  the  possible  exception  of  the  sponges, 
which  does  not  show  in  its  development  some  traces 
of  this  gastrula.  It  is  true  that  the  gastrula  is 
formed  in  many  ways  ;  it  is  true  that  it  has  a  very 
different  appearance  in  different  cases ;  that  it  is  in 
some  cases  only  dimly  suggested ;  it  is  true  that  its 
original  method  of  formation  is  still  a  matter  of 
dispute,  and  that  the  relations  of  its  various  parts  to 
the  adult  are  not  in  all  cases  settled  ;  it  even  ap- 
pears under  different  names  in  some  of  its  different 
forms  (planula — plakula).  But  these  points  only 
make  the  case  the  stronger,  for  in  spite  of  the  vari- 
ous modifying  circumstances  affecting  the  develop- 
ment, so  strong  is  the  tendency  to  inherit  this  stage, 
that  it  is  very  difficult  to  find  even  general  excep- 
tions to  the  rule.  The  significance  of  this  fact  can 
hardly  be  overrated.  For  the  embryologist  it  is  suf- 
ficient proof  that  if  we  could  correctly  follow  back 
the  history  of  animals,  we  could  trace  them  all  back 
to  a  common  ancestor  which  in  fundamental  features 
resembled  this  two-layered  sac.  And  this  represents 
the  first  multicellular  animal  which  the  evolution 
theory  assumes  ever  to  have  existed.  The  stage 
before  this  was  not  a  multicellular  animal,  but  a 
colony  of  independent  unicellular  individuals.  But 
now  the  independence  of  the  different  cells  is  lost. 
They  become  united  into  a  dependent  unity.  Some 
of  the  cells  have  one  duty  to  perform  for  the  whole 
colony,  and  others  have  a  different  function.  One  set 
of  cells  does  all  of  the  digesting,  and  another  has 
the  function  of  sensation,  etc.  A  division  of  labor 


158  E  VOL  UTION  OF  TO-DA  Y. 

has  arisen,  and  this  gastrula  represents  for  our  em- 
bryologists  the  first  multicellular  animal  which  ever 
existed,  and  which  was,  therefore,  the  common  an- 
cestor of  all  animals  now  living,  with  perhaps  the 
exception  of  the  sponges. 

If  it  be  asked  whether  this  hypothetical  ancestor 
is  represented  by  fossils,  the  answer  is  that  it  is  not 
and  doubtless  never  will  be  ;  its  body,  having  no 
hard  parts,  could  not  possibly  have  been  preserved, 
If  it  be  asked  whether  it  is  a  purely  hypothetical 
form,  unlike  any  thing  existing  to-day,  the  answer 
is,  while  the  gastrula  as  such  does  not  exist  to-day  as 
an  adult  animal,  there  are  some  ccelenterates  which 
approach  quite  close  to  it  and  are  to  be  considered 
as  direct  modifications  of  this  ancestor. 

The  Separation  of  the  Sub-Kingdoms. 

Thus  far  we  have  been  able  to  trace  the  embry- 
ology of  all  animals  over  the  same  road,  but  we  can 
do  this  no  farther.  From  the  gastrula  the  different 
large  groups  depart  in  different  directions.  This 
point  has  only  of  late  years  been  recognized.  The 
understanding  of  the  animal  kingdom  at  the  first  of 
the  century  was  such  that  all  of  the  different  groups 
were  placed  in  linear  order  one  above  the  other. 
If  this  were  true  the  embryology  of  the  higher  ani- 
mals ought  to  be  much  the  same  as  that  of  the 
lower  ones,  as  far  as  the  adult  condition  of  the 
latter.  But  this  idea  proved  palpably  untenable,  and 
soon  was  replaced  by  the  conception  of  the  animal 
kingdom  under  the  form  of  a  tree,  whose  branches, 
as  we  go  downward,  continually  unite  into  large 


SEPARA  TION  OF  THE   SUB-KINGDOMS.        1 59 

ones  and  finally  into  a  common  trunk.  And  studies 
since  Darwin  have  tended  to  show  that  the  gas- 
trula  is  the  representative  of  this  common  trunk, 
and  that  from  it  all  of  the  great  groups  branched  off 
directly.  It  is  one  of  the  problems  now  before 
embryologists  to  decide  as  to  the  number  of  the 
branches  which  arose  from  this  ancient  ancestor, 
whether  indeed  the  meaning  of  the  groups  which 
we  recognize  as  sub-kingdoms,  is  not  that  each  rep- 
resents one  of  these  branches  from  the  gastrula,  and 
if  so  to  determine  how  many  sub-kingdoms  we 
should  find.  For  instance,  whether  the  Arthropoda 
(insects,  etc.)  and  Annelids  (worms)  should  be  regard- 
ed as  separate  branches,  or  whether  they  arose  in 
common  from  the  gastrula  and  soon  separated  from 
each  other. 

This  early  divergence  of  the  great  types  from 
each  other  is  one  of  the  important  deductions  of 
recent  embryology,  since  it  enables  us  to  meet  one 
of  the  problems  we  discoursed  in  the  last  chapter, 
viz.:  the  simultaneous  appearance  of  the  types  in 
the  Silurian.  One  extreme  view  derives  seven  or 
eight  branches  directly  from  the  ancient  common 
ancestor:  I  coelenterates,  2  polyzoa  and  brachio, 
pods,  3  annelids,  4  arthropods,  5  mollusks,  6  echino- 
derms,  7  vertebrates,  and  perhaps  another  to 
include  the  heterogeneous  group  vermes.  Now  if 
any  such  conclusion  as  this  is  right,  we  immediately 
find  an  explanation  for  the  Silurian  fauna.  All  of 
the  types  which  have  been  found  in  the  Silurian 
rocks  developed  independently  and  simultaneously 
from  the  ancient  common  ancestor;  and  it  is  no 


1 60  E  VOL  UTION  OF  TO-DA  Y. 

longer  a  surprise  that  when  the  Silurian  age  opened 
they  were  all  found  well  developed.  It  is  more  of 
a  surprise  that  we  do  not  find  the  vertebrates  as 
well  developed  as  the  rest. 

It  is  evident  that  we  cannot  trace  the  common 
embryology  of  animals  beyond  this  gastrula.  If  we 
wish  to  go  farther  we  must  follow  the  sub-kingdoms 
separately.  The  difficulty  increases  as  we  attempt 
to  take  another  step.  In  some  way  this  gastrula 
was  modified  in  various  directions  to  give  rise  to 
the  various  sub-kingdoms,  but  the  embryological 
record  has  been  so  much  modified  as  to  make  it  at 
present  hardly  possible  to  follow  the  history.  In  a 
few  cases  it  can  be  done  (coelenterates,  annelids, 
mollusks)  but  as  a  rule  it  is  impossible ;  in  most 
cases  we  find  that  our  evidence  leaves  a  chasm 
between  the  gastrula  and  the  earliest  form  which 
can  be  regarded  as  showing  an  approximation 
toward  the  anatomy  of  the  sub-kingdom  to  which 
the  embryo  belongs.  All  sorts  of  suggestions  have 
been  offered  as  to  the  filling  of  this  chasm  by  the- 
ories regarding  the  exact  manner  in  which  the  gas- 
trula was  elongated  or  expanded  to  form  the  various 
types  arising.  The  vertebrates  have  received  the 
most  attention,  and  here  theories  are  particularly 
abundant.  But  every  thing  is  as  yet  only  hypotheti- 
cal and  we  need  not  take  the  trouble  to  examine  the 
question. 

After  passing  this  chasm  we  can  once  more  reach 
sure  footing.  We  now  find  that  embryos  have  as- 
sumed various  forms,  each  conforming  to  the  type 
of  its  own  sub-kingdom.  It  is  not  our  purpose  to 


SUMMAR  y.  161 

attempt  to  follow  the  various  lines.  The  general 
history  of  the  various  groups  is  essentially  alike. 
The  embryos  are  at  first  fundamentally  similar,  but 
they  soon  become  unlike,  the  time  of  separation  de- 
pending on  the  closeness  of  relation  of  the  adults. 
The  more  distant  the  relation  of  the  adults,  the 
earlier  the  embryo  separates.  The  general  embryo- 
logical  history  of  all  divisions  is  thus  parallel  to  their 
arrangement  in  a  scheme  of  classification,  a  parallel 
which  is  always  subject  to  modifying  circumstances, 
as  we  have  already  seen. 

Vegetable  Embryology. 

The  embryology  of  plants  is  of  little  importance, 
since  it  illustrates  none  of  the  significant  principles 
found  in  developing  animals.  The  organization  of 
plants  is  so  simple  that  an  extended  history  would 
be  impossible,  and  seeds,  moreover,  are  almost  uni- 
versally supplied  with  abundant  food.  Add  to  this 
the  fact  that  the  embryology  of  plants  and  animals 
has  been  studied  in  a  very  different  manner  and  for 
different  purposes,  and  we  discover  the  reason  why 
the  vegetable  kingdom  gives  us  practically  no  evi- 
dence from  its  developing  embryos. 

Summary. 

We  have  seen  that  the  study  of  adult  anatomy 
leads  to  an  arrangement  of  the  relations  of  groups 
in  the  form  of  a  branching  tree.  While  it  is  evident 
that  this  arrangement  must  be  accepted,  it  is  equally 
plain  that  the  study  of  adult  anatomy  alone  will 
never  enable  us  to  unite  the  various  sub-kingdoms 


1 62  EVOLUTION"  OF  TO-DAY. 

with  each  other.  Adult  anatomy  seems  to  teach 
that  although  the  various  types  are  nearer  together 
at  the  bottom  than  they  are  at  the  top,  yet  there  is 
no  evidence  to  show  that  they  are  united.  And  the 
same  result  arises  from  the  study  of  fossils;  for 
while  undoubtedly  the  record  of  paleontology  does 
prove  convergence  of  lines  and  the  union  of  many 
smaller  groups,  the  great  types  are  as  distinct  from 
each  other  at  the  earliest  times  of  which  we  have 
any  record  as  they  are  now.  While,  therefore,  such 
studies  indicate  the  common  union  of  the  animal 
kingdom  at  a  starting-point,  they  leave  it  only  a 
matter  of  inference. 

The  first  assistance  which  embryology  gives 
toward  a  solution  of  the  animal  kingdom,  is  in 
completing  this  chain  of  evidence.  A  long  and 
careful  study  of  development  has  brought  to  light 
the  marvellous  fact  that  the  embryology  of  the  in- 
dividual is  a  brief  repetition  of  the  past  history  of 
the  race,  a  law  which,  subject  to  certain  limitations 
already  discussed,  is  found  to  be  in  complete  har- 
mony with  the  facts  as  now  known.  The  existence 
of  this  law  is  the  argument  of  real  significance  which 
embryology  has  to  offer,  for  it  is  a  law  readily  follow- 
ing from  the  descent  theory,  but  unintelligible  other- 
wise. Using  this  law  to  interpret  the  past,  it  is 
found  that  all  animals  start  together  at  a  com- 
mon point,  all  begin  life  to-day  as  a  unicellular 
ovum.  Not  only  this,  but  for  some  distance  they 
can  be  followed  over  the  same  road,  until  a  stage  is 
reached  which  is  called  the  gastrula.  Now  if  the 
parallel  means  any  thing,  this  indicates  that  all  ani- 


SUMMARY.  163 

mals  had  a  common  history  up  to  the  time  of  the 
appearance  of  the  first  multicellular  animal,  i.  e.y  the 
first  animal  in  which  the  cells  had  ceased  to  be  in- 
dependent, and  had  formed  a  unity,  the  various 
parts  having  different  functions.  From  this  point 
there  is  a  divergence  in  many  directions.  And  here 
the  embryological  evidence  is  lacking,  for  we  can- 
not yet  tell  to  how  many  lines  of  descendants  this 
common  ancestor  gave  rise,  nor  what  were  the  sort  of 
changes  which  converted  this  form  into  the  sub- 
kingdoms  which  came  from  it.  There  is,  then,  at 
this  point,  a  gap  which,  as  yet,  cannot  be  filled  with 
any  reliable  stages.  But  the  existence  of  this  gap 
does  not  detract  from  the  all-important  conclusion 
that,  by  means  of  embryological  evidence,  it  is  pos- 
sible to  demonstrate  a  common  starting-point  of 
even  the  most  diverse  branches  of  the  animal  king- 
dom. 

A  second  method  by  which  embryology  has  as- 
sisted in  bringing  about  an  understanding  of  the 
animal  kingdom  is,  by  enabling  the  naturalist  to 
discover  the  direction  of  development  taken  by  the 
various  orders  within  the  types ;  or,  in  other  words, 
to  discover  the  relation  of  the  different  divisions  of 
the  various  sub-kingdoms  to  each  other.  In  this 
task  collateral  evidence  can  be  obtained  for  some 
groups  from  fossils.  The  amount  of  evidence  of  all 
kinds  is  constantly  increasing,  and  although,  as  yet, 
it  is  quite  insufficient  for  the  final  solution  of  many 
questions,  the  general  tendency  is  all  in  the  s,ame 
direction.  Leaving  the  gastrula  and  passing  the 
gap  we  have  mentioned,  the  next  step  is  the  appear- 


1 64  E  VOL  UTION  OF  TO-DA  Y. 

ance  in  various  embryos  of  the  characteristics  which 
mark  it  as  belonging  to  one  of  the  various  types.  A 
rudimentary  nervous  system  appears,  indicating  the 
vertebrate  type  ;  a  peculiar  mesoderm  indicates  the 
echinoderm  sub-kingdom,  etc.  Next,  it  is  seen  that, 
having  general  characteristics,  the  embryo  assumes 
those  of  the  class  to  which  it  belongs.  The  verte- 
brate ceases  to  be  a  vertebrate  in  general,  and  be- 
comes a  fish  or  mammal ;  the  echinoderm  becomes 
a  star-fish  or  sea-urchin.  Next  follow  the  charac- 
ters of  the  order — the  sub-order, — and,  as  develop- 
ment proceeds,  the  family,  and  finally  the  genus  and 
species,  the  last  distinction  frequently  not  appearing 
until  the  fully  adult  condition  is  reached. 

Embryology,  therefore,  forms  the  final  link  in  the 
chain  of  evidence  which  proves  that  there  is  a  funda- 
mental unity  in  the  organic  world,  for  the  fact  that 
embryology  repeats  past  history  proves  that  there  is 
some  unitary  bond  uniting  the  present  with  the  past. 
Evolution  offers  heredity  and  descent  as  an  explan- 
ation of  this  bond,  and  although  this  is  not  the  only 
possible  explanation,  it  is  certainly  the  simplest,  and 
the  only  one  yet  offered  which  is  founded  on  natural 
law ;  and  while  with  advancing  knowledge  the  evi- 
dence is  growing  more  complicated  and  difficult  to 
understand,  there  cannot  be  the  slightest  doubt  that 
it  is  becoming  continually  more  and  more  clear  that 
this  explanation  is  adequate  to  meet  the  facts. 


CHAPTER  V. 

GEOGRAPHICAL   DISTRIBUTION. 

THE  geographical  distribution  of  animals  on  the 
world  to-day  is  another  source  of  collateral  evidence 
as  to  the  origin  of  species.  It  is  of  particular  interest, 
since  it  was  the  study  of  this  subject  which  first  led 
Darwin  to  the  theories  which  have  made  his  name 
immortal.  It  was  this  same  class  of  facts  also,  accu- 
mulated by  years  of  travel,  which  led  Alfred  Wallace 
independently  to  conclusions  similar  to  those  of 
Darwin.  To-day,  it  is  still  the  subject  of  geograph- 
ical distribution  which  offers  some  of  the  most  con- 
vincing proofs  of  the  modification  of  species,  while 
at  the  same  time  it  presents  some  of  the  most  puz- 
zling problems  for  solution. 

The  subject  is  one  of  the  greatest  complexity,  for 
not  only  are  the  species  to  be  studied  very  numerous, 
but  the  various  causes  acting  in  the  past  and  present 
to  alter  the  distribution  of  any  species  are  almost 
infinite.  Consider  how  little  it  takes  to  produce  a 
change  in  the  fauna  and  flora  of  a  given  locality. 
The  introduction  of  a  few  English  sparrows  into  the 
United  States  has,  in  a  very  few  years,  caused  great 
changes  in  our  animals,  driving  away  and  almost 
exterminating  some  American  birds.  The  increase 
in  the  cultivation  of  the  potato  has,  in  a  short  time, 
165 


1 66  EVOLUTION  OF  TO-DAY. 

extended  the  range  of  the  Colorado  potato-beetle 
from  small  localities  of  the  West  over  almost  the 
whole  of  our  country,  and  even  into  Europe.  The 
presence  of  the  tsetze-fly  in  Africa  makes  large  terri- 
tories uninhabitable  by  cattle,  which  are  found  both 
north  and  south  of  the  infested  regions.  Many 
plants  depend  upon  insects  who  carry  their  pollen 
from  one  to  the  other.  The  insects  are  dependent 
on  the  insectivorous  birds,  and  these  upon  the 
abundance  of  bird-eating  mammals.  When  we  con- 
sider the  multitudes  of  such  modifying  conditions 
which  are  known,  it  becomes  evident  that  there 
must  be  even  greater  numbers  unknown  and  un- 
thought  of.  The  accidental  introduction  of  new 
animals  into  an  old  country ;  the  slightest  changes 
in  climate;  the  changes  in  the  course  of  river-beds; 
the  disappearance  or  growth  of  forests;  the  abun- 
dance or  absence  of  certain  kinds  of  food ;  changes 
in  the  level  of  the  land ;  the  removal  of  slight  bar- 
riers which  have  prevented  free  migration  between 
contiguous  localities; — all  of  these  circumstances 
produce  profound  modifications  in  the  inhabitants 
of  any  country,  and  teach  us  that  we  must  not  be 
surprised  if  it  is  frequently  impossible  to  say  why 
any  animal  is  found  in  one  locality  and  not  in  the 
neighboring  ones.  Moreover,  the  present  distribu- 
tion must  be  dependent  on  the  past,  and  we  know 
too  little  of  past  history  to  give  any  hope  of  a  com- 
plete explanation. 

Animals  not  Distributed  According  to  Climate. 

It  might  have  been  supposed,  indeed  would  nat- 
urally follow  from  the  standpoint  of  special  crea- 


DISTRIBUTION  OF  ANIMALS.  l6/ 

tion,  that  animals  are  exactly  adapted  to  the  locali- 
ties they  inhabit ;  and  that  the  reason  that  different 
localities  have  different  species  is  because  they  have 
different  climate,  etc.  But  this  is  not  found  to  be 
true.  Of  course  there  is  some  general  relation  of  ani- 
mals to  climate.  Those  accustomed  to  an  Arctic  cli- 
mate are  never  found  in  the  tropics,  and  those  belong- 
ing to  forests  are  never  found  in  the  open  plains. 
It  is  by  no  means  true,  however,  that  localities 
differ  in  their  inhabitants  simply  because  of  differ- 
ences in  conditions.  There  are  many  cases  where 
localities  with  almost  identical  physical  conditions 
have  utterly  different  animals  and  plants.  South 
America  has  a  very  varied  climate,  and  many  locali- 
ties could  be  picked  out  which  would  match  exactly, 
in  their  physical  conditions,  localities  of  Africa ; 
and  yet  their  fauna  and  flora  are  very  unlike.  Nor 
is  this  all,  for  there  is  abundant  proof  that  the  New 
World  is  as  well  adapted  for  Old-World  species  as  is 
their  native  home.  For  instance,  America  pos- 
sessed, when  discovered,  no  member  of  the  horse 
family,  but  as  soon  as  this  animal  was  introduced 
by  the  Spaniards,  it  ran  wild,  and  increased  with 
marvellous  rapidity,  and  now  exists  in  enormous 
numbers;  indicating  clearly  that  the  absence  of 
the  horse  from  the  western  continent  was  not  due 
to  adverse  physical  conditions.  An  even  better 
illustration  is  Australia.  This  strange  land  has  a 
highly  peculiar  indigenous  fauna,  consisting,  as  far 
as  mammals  are  concerned,  entirely  of  marsupials 
and  monotremes.  But  this  is  not  because  the  land 
is  not  fitted  for  other  animals,  for  every  European 


1 68  EVOLUTION  OF  TO-DAY. 

species  which  has  been  introduced  has  flourished,  and 
has  caused  more  or  less  extinction  of  the  native 
tribes.  The  people  have  a  saying  illustrative  of 
this.  "  As  the  white  man's  rat  has  driven  away  the 
native  rat,  as  the  European  fly  drives  away  our 
own,  and  the  clover  kills  our  fern,  so  will  the  Maori 
disappear  before  the  white  man  himself."  All  such 
instances,  which  are  numerous  enough,  show  that 
species  are  not  created  especially  for  the  locality 
they  inhabit,  since  many  localities  are  better  adapted 
to  other  animals  than  those  which  now  inhabit 
them,  and  since  some  species  flourish  better  in  other 
localities  than  those  in  which  they  are  found.  Cli- 
mate is  a  factor  in  regulating  distribution,  but  since 
like  habitats  may  possess  unlike  fauna  and  unlike 
habitats  possess  like  fauna,  it  is  evident  that  the 
influence  of  climate  is  only  secondary. 

Laws  of  Distribution  which  would  Follow  from  the 
Descent    Theory. 

All  that  can  be  expected  from  evidence  on  this 
subject  is  that  the  distribution  of  animals  is  such  as 
would  have  resulted  if  the  descent  theory  were  true, 
and  this  will,  of  course,  be  only  an  indirect  argu- 
ment. Let  us  then  first  notice  certain  laws  of  dis- 
tribution which  the  evolution  theory  demands  and 
without  which  it  cannot  stand. 

•  (i)  It  follows  from  the  descent  theory  that  allied 
species  should  inhabit  neighboring  localities.  If 
species  are  simply  exaggerated  varieties,  and  genera 
exaggerated  species,  it  would  follow  that  they  must 
have  a  regular  distribution.  A  given  species  must 


LAWS  OF  DISTRIBUTION.  169 

have  arisen  in  some  definite  and  usually  restricted 
locality,  either  slowly  or  suddenly  by  a  change  in 
the  conditions  of  its  ancestors.  This  locality  must 
then  be  the  centre  of  distribution.  It  may  subse- 
quently extend  its  range  so  as  to  cover  eventually 
a  large  area.  But  evidently  this  area  must  be,  at 
first,  a  continuous  one,  such  as  may  be  accounted 
for  by  migration,  for  we  cannot  expect  the  same 
species  to  arise  in  two  localities  independently.  If, 
therefore,  we  find  the  same  species  in  two  widely 
separated  localities,  evolution  must  assume  that  it 
formerly  also  inhabited  the  intermediate  tract  of 
country,  and  that,  owing  to  causes  which  can  seldom 
be  explained,  it  has  disappeared  from  the  inter- 
mediate regions,  while  it  still  remains  at  the  ex- 
tremes. If,  for  instance,  the  central  States  of  our 
country  should  cease  to  cultivate  the  potato,  the 
potato-beetle  would  disappear  from  this  region,  while 
still  continuing  to  live  in  the  West  and  the  East ;  and 
we  should  thus  have  a  case  of  a  single  species  in- 
habiting two  separated  localities.  The  same  prin- 
ciples would  be  true  in  regard  to  the  distribution  of 
genera,  although  here  they  would  be  less  exact, 
since  the  greater  age  of  the  genera  would  give 
greater  chance  for  wide  distribution  and  extinction  ; 
but  we  should  still  look  for  the  distribution  of  the 
species  of  a  genera  corresponding  to  their  relation 
to  each  other.  In  the  case  of  families,  still  greater 
range  of  variation  would  be  expected,  since  they  are 
doubtless  very  old,  and  have  had  time  during  their 
existence  to  migrate  to  all  parts  of  the  globe,  and  to 
have  become  extinct  in  many  localities.  It  will  cause 


I7O  EVOLUTION  OF  TO-DAY. 

no  surprise,  therefore,  if  the  different  genera  of  the 
same  family  should  be  found  to  be  sometimes  widely 
separated  from  each  other,  particularly  if  fossil  evi- 
dence show  that  the  intermediate  localities  were 
formerly  also  occupied  by  the  family.  Larger  groups 
than  families  are  so  old  that  no  geographical  rela- 
tions could  be  predicted.  (2)  It  would  necessarily 
follow  that  barriers,  which  limit  the  migration  of  a 
species,  must  be  the  limits  of  the  extension  of  the 
species.  The  same  species  ought  not  to  be  found  on 
both  sides  of  such  a  barrier,  unless  it  can  be  shown 
that  the  barrier  in  question  is  of  recent  origin,  or 
that  it  really  does  not  entirely  prevent  migration. 
(3)  The  theory  would  require  a  close  relationship 
between  the  present  and  past  inhabitants  of  any 
country,  since  the  latter  have  descended  from  the 
former.  This  would,  therefore,  make  it  desirable 
that  a  direct  relation  should  be  found  between  the 
present  inhabitants  of  any  locality  and  its  recent  fos- 
sils, after  making  deductions  due  to  recent  migra- 
tions. Geographical  distribution  should  thus  be  a 
science  by  which  the  localities  of  species,  genera,  etc., 
could  be  explained  from  the  consideration  of  the 
relationships  and  powers  of  migration  of  the  organ- 
isms, and  the  changes  in  the  configuration  and 
climate  of  the  land.  Anatomical  relationship  should 
be  parallel  with  geographical  relationship.  Unless 
these  laws  are  found  to  be  verified  with  more  or  less 
exactness,  it  would  be  impossible  to  accept  evolu- 
tion ;  if  they  are  verified,  evolution  finds  a  certain 
amount  of  support. 


PRESENT  AND  PAST.  1?I 

The  Relation  of  the  Present  to  the  Past. 
Speaking  in  general  terms,  it  is  found  that  the 
species  of  the  most  recent  geological  deposits  are 
identical  with  those  now  living,  although  there  are,  of 
course,  thousands  of  species  now  living  which  have 
never  been  found  as  fossils.  Rocks  somewhat  older 
contain  fossils  related  to  existing  forms,  but  specifi- 
cally distinct ;  and  going  still  farther  back,  the  rela- 
tions become  less  and  less  close,  until  finally  we 
reach  a  fauna  very  different  from  that  existing  to- 
day. All  of  this  is,  of  course,  compatible  with  any 
theory  of  the  organic  world  that  we  may  form, 
agreeing  equally  well  with  special  creation  or  with 
evolution.  But  when  closely  examined  the  facts  are 
more  significant.  If  the  fossils  of  any  one  locality, 
sufficiently  isolated  to  prevent  free  migration,  be 
compared  with  its  living  animals,  a  striking  likeness 
is  seen.  For  example  :  it  is  found  that  the  fauna 
of  South  America  is  peculiar  in  possessing  a  great 
number  of  the  remarkable  order  of  Edentata  (arma- 
dillos, etc.),  animals  found  nowhere  else  in  the  world, 
with  the  exception  of  one  quite  different  form  in 
Africa.  Now  the  fossils  of  North  and  South  Amer- 
ica are  also  remarkable  in  possessing  great  numbers  of 
Edentates,  which  will  therefore  naturally  be  looked 
upon  as  the  ancestors  of  the  present  species.  An- 
other illustration  is  offered  by  the  primates  of  the 
New  and  the  Old  worlds.  The  New-World  monkeys 
are  very  different  from  those  of  the  old  world,  al- 
though, so  far  as  we  can  see,  there  is  no  reason  for  this 
in  the  physical  conditions  of  the  two  worlds;  but  the 
species  of  the  one  locality  form  a  very  distinct  group, 


1/2  EVOLUTION  OF  TO-DAY. 

which  is  radically  separated  from  those  of  the  other. 
And  South  American  fossil  monkeys  are  similar  to 
the  present  animals  found  there ;  while  the  fossils 
of  Europe  are  closely  related  to  the  order  of  Old- 
World  monkeys  now  existing.  Perhaps  the  best 
illustration  of  this  principle  is  afforded  by  Australia. 
This  strange  land  has  no  mammals  except  marsupi- 
als, and,  as  we  come  to  study  the  fossils  of  the 
country,  we  find  that  they  in  like  manner  comprise 
numerous  marsupials,  but  no  other  mammals,  and 
these  marsupial  fossils  are  of  such  a  structure  as  to 
show  a  close  relation  to  existing  species.  It  cannot, 
of  course,  be  claimed  that  the  present  species  were 
created  so  closely  related  to  the  older  inhabitants, 
because  the  climate  of  Australia  is  especially 
adapted  to  this  form  of  animal ;  for,  as  we  have 
already  noticed,  almost  every  European  mammal  is 
able,  not  only  to  exist  in  Australia,  but  also  to  ex- 
terminate the  native  inhabitants.  But  geology 
readily  explains  this  peculiar  fauna.  Australia  was 
formerly  connected  with  Asia  at  a  time  when  the 
latter  continent  was  filled  with  marsupials.  But  the 
connection  was  soon  lost,  and  when  higher  mammals 
appeared  in  Europe  and  Asia  they  were  unable  to 
get  into  the  now  separated  Australia.  The  marsu- 
pials which  this  land  had  originally  received  from 
the  north,  had  the  whole  continent  to  themselves, 
and  they  therefore  multiplied  and  expanded,  giv- 
ing rise  to  the  present  marsupial  fauna,  unmolested 
by  any  of  the  higher  mammals  which  were  develop- 
ing on  the  other  continents.  And  numerous  other 
instances  could  be  given,  showing  conclusively  that 


PRESENT  AND  PAST.  173 

when  any  country  possesses  a  peculiar  fauna,  the 
fossils  indicate  that  the  same  peculiarity  existed  in 
times  past,  although  it  usually  happens  that  no 
species  found  to-day  exists  as  a  fossil.  That  this 
fact  is  an  indication  of  genetic  connection  between 
the  present  and  the  past,  is  evident  enough. 

When,  however,  we  examine  the  great  bulk  of 
species  on  our  larger  continents,  we  soon  discover 
that  the  present  distribution  of  many  of  them  is  by 
no  means  similar  to  that  of  their  fossil  representa- 
tives. Many  animals  now  confined  to  small  locali- 
ties formerly  ranged  widely.  Species,  genera,  and 
families  which  have  in  the  past  wandered  to  and 
fro  with  varying  conditions,  have  become  extinct 
to  such  an  extent  as  to  obscure  the  general  relation 
just  noticed.  Horses,  for  instance,  were  not  found 
in  America  when  discovered,  although  fossils  tell  us 
that  they  did  exist  here  in  the  very  recent  geological 
times.  Fossil  camels  appear  in  our  rocks,  although 
no  living  camel  belongs  to  the  New  World.  Ameri- 
ca formerly  had  a  fauna  composed  of  elephants,  hip- 
popotamuses, tapirs,  and  hosts  of  other  animals  now 
found  in  Africa  or  India.  All  this  is,  however,  not 
surprising,  for  migration  and  extinction  have  been 
abundant.  If  it  had  appeared  that  America  when 
discovered  possessed  a  large  family  of  horses,  while 
its  fossils  showed  no  trace  of  them  it  would  haye 
presented  serious  trouble  ;  but  no  case  of  this  kind 
is  forthcoming. 

In  this  connection  has  appeared  one  result  of 
special  interest.  The  study  of  the  fossils  of  North 
America  and  Europe  discloses  the  fact  that  only  a 


174  EVOLUTION  OF  TO-DAY. 

short  time  before  the  present  geological  epoch  the 
northern  continents  possessed  a  fauna  very  different 
from  that  now  found  there.  Over  Europe  lived  a 
fauna  closely  resembling  that  now  found  in  Africa 
and  India,  and  North  America  similarly  contained 
animals  now  belonging  to  South  America.  At  this 
time  the  northern  and  southern  continents  differed 
very  little  from  each  other.  Elephants,  giraffes, 
hippopotamuses  lived  all  through  Europe;  tapirs, 
great  tigers,  llamas,  edentates,  existed  in  great 
numbers  in  North  America.  Since  that  time  there 
has  been  a  remarkable  change,  and  one  which 
appears  to  have  been  quite  sudden.  But  it  is  a  change 
which  has  received  a  happy  explanation,  for  this 
wide  distribution  of  tropical  animals  occurred  just 
before  the  glacial  period.  Geologists  have  agreed 
that  not  long  before  the  present  era  the  northern 
parts  of  the  northern  continents  were  covered  with 
great  sheets  of  ice  which  gradually  travelled  south- 
ward, covering  much  of  Europe  and  North  America, 
and  producing  great  physical  changes  of  every  kind. 
This  southward  moving  glacial  mass  is  seen  at  once 
to  be  a  perfect  explanation  of  many  of  the  differen- 
ces between  the  present  fauna  of  the  northern  con- 
tinents and  that  of  older  times.  With  the  advance 
of  the  ice  and  the  consequent  fall  in  temperature,  all 
animals  and  plants  must  have  been  driven  farther 
and  farther  south.  Many  were  destroyed  alto- 
gether, not  being  able  to  find  a  suitable  climate. 
Some  were  driven  into  South  America  and  Africa, 
and,  finding  here  favorable  conditions,  they  continued 
to  live  and  multiply.  When  at  last  the  ice  once  more 


PRESENT  AND  PAST.  175 

retreated  northward  at  the  close  of  the  glacial 
period,  many  animals  would  follow  the  retreating 
ice  and  thus  once  more  come  to  inhabit  their  old 
localities.  Others  finding  the  conditions  of  their 
own  home  well  suited  to  their  needs,  did  not  return 
north,  but  remained  where  they  were,  or  even  went 
farther  south,  And  thus  the  southern  continents 
came  to  be  the  habitat  of  animals  and  plants  previ- 
ously ranging  into  the  northern  continents.  The 
glacial  period,  by  causing  extensive  migration  and 
extinction  has  profoundly  modified  the  distribution 
of  animals  and  plants. 

The  distribution  of  fossils  serves  in  many  cases  as 
a  key  to  the  present  distribution.  There  exists  a 
wonderful  relation  between  the  living  and  the  dead 
inhabitants  of  any  country.  It  is  often  possible  to 
trace  quite  exactly,  by  the  study  of  living  animals 
and  fossil,  remains,  where  a  given  order  first  arose  ; 
how  it  dispersed  in  various  directions,  reaching 
widely  separated  regions  ;  and  how,  finally,  it  became 
extinct  in  many  places,  leaving  as  its  scattered  repre- 
sentatives to-day  families  separated  by  wide  tracts 
of  land  or  sea.  For  example,  such  studies  have 
revealed  the  following  history  of  marsupials.  The 
order  arose  in  Europe  as  the  earliest  mammals  with 
which  we  are  acquainted.  From  this  point  of  origin 
they  spread  all  over  the  eastern  hemisphere,  even 
reaching  Australia,  at  that  time  connected  with 
Asia.  They  also  migrated  westward,  and  succeeded 
in  reaching  America,  by  what  means  we  do  not  at 
present  completely  understand.  But  reach  America 
in  some  way  they  did,  and  thus  the  whole  world  be- 


1/6  EVOLUTION   OF  TO-DAY. 

came  inhabited  by  marsupials.  Meantime,  there 
appeared  in  Europe  some  representatives  of  the  true 
mammals,  which  were  of  a  higher  order  than  mar- 
supials, and  quickly  began  to  contend  with  and  ex- 
terminate them.  These  new  mammals  began  to 
spread  from  their  point  of  origin  over  the  eastern 
and  western  continents  ;  destroying  the  marsupials 
as  they  came  into  competition  with  them.  They 
thus  caused  the  complete  extinction  of  the  latter 
group  over  all  the  eastern  continent  except  Aus- 
tralia, which  had  in  the  meantime  become  separated 
from  Asia.  On  the  western  continent,  too,  the  vic- 
torious mammals  destroyed  all  marsupials  except 
one  single  family,  which,  for  some  reason,  succeeded 
in  maintaining  its  existence.  This  was  the  opossum, 
which  is  found  in  North  and  South  America  ;  and 
thus  we  see  the  final  result  to  be  that,  of  the 
formerly  widely  distributed  order,  representatives 
are  left  in  only  two  localities,  separated  from  each 
other  by  half  the  globe.  All  of  this  time  the  species 
and  genera  have  been  constantly  changing,  so  that 
the  families  now  living  are  very  different  from  those 
of  the  earlier  ages.  And  so  in  other  cases.  The 
tendency  of  the  evidence  seems  to  show  that  mam- 
mals originated  in  Europe,  or  north  of  Europe,  and 
then  migrated  east,  west,  and  south,  finally  thus 
filling  the  whole  world,  except  oceanic  islands. 

Zoological  Regions. 

Turning  now  from  the  past  to  the  present,  let  us 
first  notice  how  far  anatomical  relationship  is  parallel 
with  geographical  relationship.  One  prominent  fact 


ZOOLOGICAL  REGIONS.  I// 

first  strikes  our  attention.  The  animals  of  a  single 
group,  belonging  to  one  country,  though  they  may 
consist  of  many  species,  yet  show  a  close  relation  to 
each  other,  and  thus  form  a  unit.  Every  naturalist 
who  has  had  the  opportunity  of  travel,  or  of  exami- 
ning collections  from  different  localities,  has  been 
struck  with  this  fact.  As  he  roams  through  the 
forests  of  South  America,  he  finds  many  distinct 
species  of  monkeys,  differing  much  from  each  other, 
and  yet  all  having  a  fundamental  likeness  by  which 
they  can  at  a  glance  be  distinguished  from  the 
monkeys  of  the  Old  World.  A  collection  of  beetles, 
of  birds,  or  almost  any  other  class  of  animals  shows 
a  like  result.  And  this  is  not  simply  that  the  species 
and  genera  are  different,  but  there  is  evident  funda- 
mental difference  between  the  species  of  two  separ- 
ated countries.  This  fact  has  found  recognition  with 
all  students  of  geographical  distribution,  and  has 
been  expressed  by  the  division  of  the  world  into 
zoological  regions,  in  each  of  which  the  fauna  and 
flora  are  found  to  show  a  fundamental  likeness. 
These  zoological  regions  are  always  separated  from 
each  other  by  physical  barriers,  which  effectually 
prevent  at  the  present  time  any  migration  from  one 
to  the  other,  and  although  they  sometimes  have 
identical  climate,  the  fauna  and  flora  are  always  dis- 
tinct. It  is  true  that  different  students  of  distribu- 
tion have  not  agreed  exactly  upon  the  extent,  or 
even  the  number,  of  these  regions,  their  limits 
varying  according  to  the  class  of  animals  which  is 
taken  as  a  basis  for  the  division.  Wallace,  using  the 
mammals  as  a  guide,  distinguishes  six,  while  others 


1/8  EVOLUTION  OF  TO-DAY. 

have  recognized  nine.  But  the  important  fact  is 
not  as  to  the  number  or  exact  limits  of  these  divi- 
sions, but  that  they  do  exist ;  that  it  is  everywhere 
recognized  that  organisms  are  grouped  together  in 
masses,  which  are  separated  from  each  other  by  bar- 
riers. The  details  are  a  secondary  feature. 

The  question  of  course  arises  as  to  what  is  the 
cause  of  this  bond  of  unity  found  in  the  inhabitants 
of  the  separate  zoological  regions.  Doubtless,  some 
of  it  may  be  due  to  like  conditions  affecting  all 
alike  ;  but  this  is  not  sufficient  to  explain  all.  The 
South  American  monkeys  all  have  six  molar  teeth, 
while  none  of  the  Old- World  monkeys  have  more 
than  five ;  and  surely  unlike  conditions  can  never 
account  for  this  sort  of  difference.  It  was  long  ago 
pointed  out  by  Darwin  that  the  theory  of  genetic 
descent  offers  an  explanation  for  such  facts.  Sepa- 
rated as  these  regions  are  from  each  other,  the 
species  of  any  comparatively  small,  recent  group 
will  all  be  somewhat  close  relations,  and  the  com- 
mon bond  of  union  is  that  of  inheritance.  The  first 
monkeys  reaching  South  America  from  the  north, 
for  example,  had  six  molar  teeth,  and  the  present 
species,  which  are  their  descendants,  though  in 
many  features  they  have  become  distinct,  have  re- 
tained this  feature  of  likeness ;  and  since  now  the 
physical  barriers  prevent  the  immigration  of  other 
forms,  it  results  that  all  of  the  South  American 
monkeys  show  a  fundamental  likeness.  Barriers 
will  thus  tend  to  confine  within  their  limits,  species 
somewhat  closely  related  to  each  other.  Australia 
contains  nearly  all  of  the  marsupials  of  the  world  ; 


DISTRIBUTION  OF  SPECIES  AND   GENERA.      1/9 

South  America  nearly  all  of  the  Edentates  and  flat- 
nosed  monkeys ;  Africa  all  of  the  hippopotamuses 
and  giraffes  ;  Madagascar  most  of  the  lemurs, — and 
all  of  these  facts  receive  a  ready  explanation  in 
accordance  with  the  descent  theory. 

Present  Distribution  of  Species  and  Genera. 

As  a  rule,  it  is  found  that  the  area  occupied  by 
any  species  is  a  continuous  one.  For  instance,  the 
habitat  of  the  common  European  jay  (Garrulus 
glandarius)  begins  in  the  British  isles,  and  extends 
throughout  Europe  as  far  as  the  Ural  Mountains, 
the  jay  being  common  in  this  region  everywhere 
that  the  presence  of  forests  gives  it  habitation. 
Beyond  the  Urals  it  is  never  found,  its  place  being 
supplied  by  another  species  of  the  same  genus  (G. 
brandti}.  And  this  instance  illustrates  the  very  gen- 
eral rule.  It  is  a  rule  to  which  very  few  exceptions 
occur,  hardly  more  than  a  dozen  good  examples 
being  known.  The  marsh-tit  (Parus  palustris)  is 
found  in  Southern  Europe  and  in  China,  while  the 
intermediate  country  is  inhabited  by  a  different 
species.  But  most  of  these  exceptions  are  readily 
explained,  and  only  serve  to  confirm  the  general 
rule.  A  few  peculiar  cases  will  be  noticed  further  on. 

Practically,  the  same  rule  holds  good  in  the  case 
of  genera,  continuous  generic  areas  being  almost  uni- 
versal. As  the  localities  inhabited  by  the  different 
species  of  a  genus  are  compared,  it  appears  that  they 
usually  touch  each  other  at  these  confines,  or  some- 
times overlap;  in  either  case,  making  an  unin- 
terrupted generic  distribution.  The  genus  of  true 


l8o  EVOLUTION  OF  TO-DAY. 

jays  furnishes  again  a  good  illustration.  One 
could  begin  in  the  British  isles,  travel  eastward 
to  the  Pacific  Ocean,  and  then,  turning  south, 
return  west  again,  south  of  the  Himalayas,  through 
Western  Asia  and  Northern  Africa  to  Spain,  and 
be  able  to  find  jays  in  all  of  this  region,  except 
a  few  interrupted  areas  which  do  not  form  suit- 
able habitat  for  the  genus.  The  species  has 
changed  many  times,  no  less  than  twelve  dis- 
tinct species  being  found  in  this  region ;  but  the 
specific  areas  either  touch  each  other  or  overlap. 
And  in  America  another  genus  of  jays  is  found, 
with  its  appropriate  distribution.  Exceptions  to 
this  rule  are  rather  more  numerous  than  in  the 
former  case,  and  this,  of  course,  we  would  expect, 
for  evolution  looks  upon  a  genus  as  a  highly  devel 
oped  species,  in  which  the  varieties  have  become 
distinct  enough  to  rank  as  species.  If  this  is  true, 
genera  must  be  older  than  species,  and  although 
originally  they  must  have  had  a  common,  central 
starting-point,  they  have  had  more  time  and  oppor- 
tunity for  their  dispersal  and  extinction  than  species; 
and  examples  of  discontinuity  do  occur,  although 
they  are  very  few  compared  with  the  abundance  of 
instances  of  continuity  in  generic  distribution.  One 
species  of  magpie  is  confined  to  Spain  and  Por- 
tugal, while  another  appears  in  Northeastern  Asia 
and  Japan.  One  species  of  a  mole  (Ulotrichus)  in- 
habits Japan  and  another  British  Columbia.  Two 
species  of  thrush-tit  live  in  the  Himalayas,  while 
a  third  is  confined  to  Java.  The  genus  Ritta 
(ground-thrush)  ranges  from  Hindostan  to  Aus- 


DISTRIBUTION  OF  SPECIES  AND   GENERA.      l8l 

tralia,  while  a  single  species  inhabits  West  Africa. 
And  other  good  examples  might  be  given,  all  of 
which,  from  the  fact  that  they  are  considered  re- 
markable, are  to  be  regarded  as  exceptions  to  the 
rule  which  finds  genera  confined  to  definite,  con- 
tinuous localities. 

Taking  families  now  into  consideration,  we  are 
prepared  to  find  a  much  greater  amount  of  disconti- 
nuity. Families  are  only  highly  developed  genera, 
but  so  long  ago  was  it  that  all  the  forms  of  a  given 
family  had  a  common  starting-point,  that  the  vari- 
ous genera  will  have  had  ample  opportunity  to 
wander  perhaps  all  over  the  world  ;  to  have  become 
greatly  modified  ;  to  have  completely  disappeared 
in  some  localities,  being  displaced  by  other  animals 
better  adapted  to  the  conditions  of  life ;  and  even, 
perhaps,  to  have  become  separated  by  impassable 
barriers,  which  have  arisen  since  the  '  migrations, 
such  as  recent  mountain  ranges.  We  should  there- 
fore expect  that  some  families  may  have  an  almost  cos- 
mopolitan range,  particularly  those  with  great  powers 
of  migration.  It  is  hardly  necessary  to  say  that  the 
facts  bear  out  this  expectation.  Some  families  of 
bats  and  birds  have  a  practically  world-wide  distri- 
bution ;  many  have  a  remarkably  discontinuous  area 
at  the  present  day,  although  fossils  tell  us  that  for- 
merly they  were  widely  distributed.  The  camels 
are  divided  by  the  Atlantic  Ocean,  one  genus  living 
in  Africa,  and  a  second  in  South  America.  One 
family  of  insectivora  is  found  in  Madagascar,  Cuba, 
and  Hayti.  On  the  other  hand,  there  are  a  few 
examples  of  restricted  family  areas.  The  birds  of 


1 82  EVOLUTION  OF  TO-DAY. 

paradise,  consisting  of  nineteen  or  twenty  genera 
and  thirty-five  species,  are  confined  to  New  Guinea 
and  the  adjacent  islands.  In  this  case,  it  is  neces- 
sary to  suppose  that  the  entire  family  has  arisen 
since  New  Guinea  has  been  an  island.  Neither 
continuous  nor  discontinuous  family  areas  can  be 
considered  the  rule. 

When  we  come  to  larger  groups,  the  rule  is  re- 
versed, and  continuous  restricted  areas  are  never 
found.  Orders  are  very  old  divisions,  becoming 
separated  from  each  other  at  the  very  earliest  period 
in  the  history  of  mammals,  and  no  instance  can  be 
found  where  there  has  not  been  very  wide  disper- 
sion. If  we  take  into  consideration  fossil  remains, 
there  is  hardly  an  order  which  does  not  show  world- 
wide distribution.  To-day  the  distribution  may  be 
very  different,  for  families  and  genera  have  been 
dropped  out,  leaving  the  present  ones  widely  sep- 
arated. 

In  short,  the  present  distribution  of  groups  of 
organisms  upon  our  continents  is  parallel  with 
their  anatomical  relationship  and  their  antiquity. 
Species,  which  are  of  most  recent  origin,  have  almost 
always  a  continuous  area  of  habitation,  as  if  they 
had  dispersed  from  some  central  point.  Genera, 
being  somewhat  older,  show  a  wider  distribution, 
with  more  frequent  breaks  in  the  continuity,  but 
still  give  evidence  of  a  central  point  of  origin. 
Families,  older  still,  have  ranged  much  more  widely, 
while  orders,  the  oldest  of  all,  have  had  always  a 
world-wide  distribution,  which  in  some  cases  they 
preserve,  but  in  others  have  lost  by  extinction. 


LIMITATION  BY  BARRIERS.  183 

Such  a  distribution  is  not  out  of  harmony  with  the 
view  that  species  are  specially  created — for  no  dis- 
tribution could  be  out  of  harmony  with  this  idea, — 
but  it  will  hardly  be  denied  that  the  geographical 
distribution  of  groups  indicates  a  law  of  distribu- 
tion :  a  law  unexplained  by  special  creation,  but  one 
which  must  inevitably  follow  from  the  genetic  de- 
scent of  animals  and  the  origin  of  species  from  older 
varieties. 

Do  Barriers  Limit  the  Areas  of  Specific  Distri- 
bution ? 

To  this  question  the  answer  is  that,  as  a  rule,  species 
are  not  found  on  the  opposite  sides  of  impassable 
barriers.  But  to  this  rule  there  are  some  remarkable 
exceptions  of  species  which  are  not  thus  limited  by 
seemingly  natural  barriers.  And  while  the  instances 
of  agreement  with  the  rule  outnumber  the  excep- 
tions one  thousand  to  one,  it  is  the  exceptions  to  the 
rule  which  must  occupy  our  attention.  The  most 
important  exceptions  are  the  existence  of  the  same 
species  of  fish  on  either  side  of  the  Isthmus  of 
Panama ;  the  presence  of  the  same  species  of  fresh-  , 
water  animals  on  the  two  continents ;  and  the  v 
presence  of  certain  Arctic  species  of  plants  on  the 
mountains  of  Southern  Europe  and  America.  These 
cases  will  be  taken  up,  therefore,  as  illustrations  of 
the  classes  of  difficulties  and  the  method  of  meeting 
them. 

Such  cases  of  discontinuous  distribution  are  not 
to  be  explained  by  assuming  a  formerly  wide  dis- 
persal, for  how  can  we  suppose  that  with  any 
amount  of  dispersal  the  barriers  in  question  could 


1 84  EVOLUTION  OF  TO-DAY. 

be  crossed  ?  The  only  method  of  explanation  is  to 
show  either  that  the  barriers  in  question  do  not 
act  as  rigidly  as  at  first  sight  seems,  or  to  show  that 
they  have  not  always  existed.  One  series  of  dif- 
ficulties disappears  when  we  remember  that  the 
physical  conditions  of  the  land  have  not  always 
been  what  they  are  now.  The  Pacific  Ocean  and 
the  Gulf  of  Mexico  are  now  separated  by  a  bar- 
rier impassable  to  fishes ;  but  this  has  not  always 
been  the  case.  We  have  only  to  assume  the  depres- 
sion of  the  land  a  few  hundred  feet  from  the 
isthmus,  and  we  should  have  the  two  oceans  united. 
Here  is  a  ready  explanation  of  the  first  difficulty 
mentioned.  Africa  was  once  connected  with  Eu- 
rope, though  now  it  is  practically  separated  from 
it.  Similarly  Australia  was  formerly  connected  to 
Asia.  Many  of  our  mountain  ranges  are  of  com- 
paratively recent  origin,  and  although  now  they 
form  effectual  barriers,  they  have  not  always  done 
so.  If,  therefore,  a  species  is  very  old  we  might 
find  representatives  of  it  on  either  side  of  such  a 
recently  created  barrier,  and  not  unfrequently  might 
we  find  species  of  this  same  genus  thus  separated. 

To  explain  the  class  of  facts  illustrated  by  the 
second  of  the  above  examples,  naturalists  have 
studied  with  great  care  the  means  of  dispersal  of 
animals,  with  the  result  of  proving  that  the  so-called 
barriers  are  not  always  so  rigid  in  their  action  as 
at  first  appears.  It  would  seem  that  fresh-water 
animals  would  be  very  limited  in  their  powers  of 
migration;  would  be  confined  to  a  single  river  or 
system  of  rivers.  For,  unable  to  live  in  the  air  or  in 


LIMITATION  BY  BARRIERS.  185 

the  ocean,  their  distribution  seems  at  first  an  impos- 
sibility. But  this  is  far  from  being  true  ;  for  every 
one  knows  that  fresh-water  species  are  not  thus 
limited,  and  few  would  have  the  hardihood  to 
claim  that  each  system  of  rivers  had  created  for  it  a 
pair  of  parents  for  every  species.  Indeed,  the  actual 
means  of  dispersal  from  one  body  of  fresh  water  to 
another  have  been  discovered  in  many  cases. 
Changes  of  level  in  the  land  cause  rivers  once  sepa- 
rated to  unite  either  permanently  or  temporarily ; 
and  floods  have  from  time  to  time  had  the  same 
effect  Again,  the  eggs  of  many  fresh-water  species 
can  survive  exposure  to  the  air  for  a  long  time,  and 
clinging  as  they  do  to  weeds  and  grass,  may  fre- 
quently be  carried  from  place  to  place  by  birds  or 
shaggy-haired  animals.  Nor  does  the  sea  always 
prove  an  impassable  barrier,  for  many  cases  are 
on  record  of  fresh-water  species  enduring  without 
injury,  for  a  long  time,  immersion  in  salt  water. 
Floating  ice  has  been  known  to  carry  fresh-water 
organisms  across  bodies  of  salt  water,  and  here  is  a 
means  of  communication  between  different  conti- 
nents. Particularly  significant  is  this  suggestion  when 
we  bear  in  mind  that  instances  of  fresh-water  animals 
being  found  on  both  sides  of  a  large  body  of  salt 
water,  occur  almost  exclusively  in  the  colder  regions 
of  the  world,  where  this  factor  could  come  into 
play  and  where  the  continents  approach  each  other. 
Again,  some  fresh-water  animals  can  become  accus- 
tomed to  salt  water,  and  vice  versa  ;  so  that  actual 
migration  through  the  sea  may  take  place  in  some 
instances.  And  the  significance  of  these  facts  is 


1 86  EVOLUTION  OF  TO-DAY. 

increased  when  we  learn  that  no  cases  are  known 
where  the  same  fresh-water  species  occur  on  either 
side  of  a  high  continuous  mountain  range,  except  in 
cases  where  human  agencies  have  come  into  play, 
and  one  or  two  instances  of  a  remarkable  distribu- 
tion of  some  very  old  species.  The  sea  is,  then,  not 
an  absolute  barrier  even  for  fresh-water  animals, 
and  a  certain  amount  of  similarity  of  species  in  two 
neighboring  continents  is  not  inexplicable. 

The  last  of  the  difficulties  mentioned,  viz.,  the 
agreement  of  Alpine  and  Arctic  flora,  receives  quite 
a  different  explanation.  The  glacial  period  once 
more  proves  of  assistance.  At  the  time  when  the 
glaciers  swept  down  over  Northern  Europe,  they,  of 
course,  drove  in  front  of  them  all  of  the  animals  and 
plants  of  the  north,  so  that  finally  the  southern  parts 
of  the  continents  with  an  Arctic  climate  cajne  to  be 
inhabited  by  a  species  belonging  to  the  more  north- 
ern latitudes.  When  at  last  the  ice  began  once 
more  to  retreat  northward,  the  climate  of  the  south- 
ern regions  began  to  grow  warmer,  and  the  Arctic 
species  could  not  endure  it.  Some  of  them  were 
probably  modified  to  suit  the  change  in  climate, 
giving  rise  to  new  species.  Others  followed  the  re- 
treating ice  once  more  northward,  keeping  thus  con- 
stantly in  an  Arctic  temperature ;  while  still  others, 
instead  of  going  north,  simply  ascended  the  moun- 
tains, and  in  this  way  kept  themselves  in  a  suitable 
climate.  Eventually  the  mountains  and  the  Arctic 
regions  came  to  possess  similar  species.  And  by 
extending  the  explanation,  the  occasional  likeness 
of  species  in  the  northern  and  southern  continents 


LIMITA  TION  B  Y  BARRIERS.  1 8/ 

is  accounted  for,  some  species  migrating  south  as 
well  as  north  in  search  after  a  cooler  climate.  Wal- 
lace has  very  carefully  followed  out  this  explanation 
according  to  the  accepted  principles  of  geology,  and 
finds  it  a  happy  explanation  for  great  masses  of 
peculiar  facts. 

But,  with  all  of  these  suggestions,  we  must  not 
imagine  that  the  difficulties  are  removed ;  many 
facts  still  remain  for  which  no  sufficient  explanation 
has  been  given.  Most  of  them  are  isolated  cases, 
each  of  which  must  demand  its  own  separate  expla- 
nation, and  they  are  certainly  becoming  fewer  in 
numbers  as  we  become  more  acquainted  with  the 
present  and  past  history  of  animals.  Probably  the 
greatest  difficulties  which  the  present  distribution 
of  animals  offers  to  the  descent  theory,  concern  the 
wide  disf>ers*al  of  fresh-water  organisms.  Even 
when  we  have  granted  all  that  is  claimed  as  to  the 
occasional  means  of  dispersal  by  changes  in  the 
level  of  the  land,  by  floods,  by  transportation  of  eggs, 
by  whirlwinds,  by  floating  ice,  etc., — even  when  we 
have  granted  that  these  means  have  accomplished 
much,  it  still  remains  a  marvellous  fact  that  a  cer- 
tain fresh-water  fish,  Galaxias  attenuatus,  is  found 
in  the  rivers  of  Tasmania,  New  Zealand,  the  Falk- 
land Isles,  and  the  mainland  of  South  America. 
How  to  explain  such  a  case  as  this,  it  is  difficult  to 
say,  unless  it  be  regarded  as  a  case  where  a  former 
species  of  almost  universal  distribution  has  become 
extinct  except  in  these  localities ;  and  this  explana- 
tion is  any  thing  but  a  happy  one.  A  similar, 
though  less  striking,  puzzle  is  offered  by  the  occur- 


1 88  EVOLUTION  OF  TO-DAY. 

rence  of  the  same  species  of  fresh-water  hydra  in  the 
'rivers  of  the  two  hemispheres.  The  wide  distribu- 
tion of  land  animals  is  sometimes  equally  surprising. 
Two  species  of  the  genus  tapir  occur  in  South 
America,  and  another  in  the  Moluccas.  The  tro- 
gon,  a  gorgeously  colored,  insect-eating  bird,  is 
abundant  in  Asia  and  Africa,  and  a  single  genus  is 
found  in  South  America.  Two  species  of  anthro- 
poid apes  are  found  in  West  and  Central  Africa,  and 
two  others  in  Sumatra.  All  such  cases  as. these, 
though  not  insuperable  difficulties,  are  rather  puz- 
zling. The  distribution  of  the  edentates  offers  per- 
haps the  hardest  problem  of  all.  These  animals 
appeared  in  South  America,  Africa,  and  Asia  long 
before  they  did  in  North  America.  And  since  we 
can  see  no  means  by  which  South  America  could 
have  received  its  inhabitants  except  through  North 
America,  it  is  very  surprising  to  find  edentates  in 
the  former  country  earlier  than  in  the  latter.  To 
solve  this  puzzle,  some  naturalists  have  not  hesitated 
to  assume  a  hypothetical  continent  which  formerly 
united  Africa  and  South  America ;  while  others, 
among  whom  are  Huxley  and  Wallace,  suppose  that 
there  once  existed  a  tract  of  land  in  the  northern 
Pacific  which  was  the  birthplace  of  the  edentates, 
and  which  being  connected  at  times  with  South 
America  and  Asia,  furnished  them  with  their  supply 
of  this  order.  Negative  evidence  in  paleontology  is, 
however,  of  little  value,  and  it  may  yet  be  found  that 
North  America  had  its  edentates  earlier  than  the 
southern  continent ;  but  at  present  we  do  not  know 
what  to  do  with  this  case.  Something  of  a  surprise, 


OCEANIC  ISLANDS.  189 

too,  is  it  to  find  that  America,  when  discovered,  pos- 
sessed no  horses,  a  family  which  geology  tells  us 
originated  here,  and  which  did  exist  until  recent 
times,  and  for  which  the  country  was  most  admira- 
bly fitted,  as  has  been  since  proved.  Though  some- 
what surprising  to  find  this  so,  it  is  not  to  be  won- 
dered at  that  we  are  ignorant  as  to  the  cause  of  this 
sudden  extinction,  for  we  know  almost  nothing  of 
the  surroundings  of  the  past.  Difficulties  there  are, 
then,  and  some  of  them  very  puzzling  ones ;  but,  as 
a  rule  followed  in  a  vast  majority  of  cases,  the  dis- 
tribution of  animals  on  our  continent  is  such  as  can 
be  explained  according  to  the  supposition  that  spe- 
cies, genera,  families,  etc.,  have  all  arisen  at  central 
points,  and  have  from  here  dispersed  in  various 
directions,  giving  rise  constantly  to  new  forms. 

Oceanic  Islands. 

All  the  cases  thus  far  considered  are  animals  on 
continents.  But  there  are  many  tracts  of  land  in 
the  ocean  which  are  not  and  never  have  been  con- 
nected with  the  mainland.  Most  of  them  are  vol- 
canic in  their  origin  and  are  situated,  at  least  this 
is  true  of  the  so-called  oceanic  islands,  not  less 
than  five  hundred  miles  from  the  neighboring 
continents.  Now,  such  islands  have  their  own  in- 
habitants. The  first  question  is,  of  course,  as  to 
where  their  original  inhabitants  came  from.  Only 
two  answers  to  this  question  are  possible.  Either 
they  were  especially  created  for  these  islands,  or 
they  have  been  derived  from  the  neighboring  main- 
lands. Upon  the  former  supposition  we  should  not 


1 90  E  VOL  UTION  OF  TO-DA  Y. 

be  able  to  make  any  predictions  as  to  oceanic-island 
life,  except  to  expect  that  we  might  find  either  the 
same  species  as  those  found  on  the  mainland,  or 
some  entirely  different.  But  upon  the  latter  suppo- 
sition, which  is,  of  course,  the  more  probable,  and 
which  is  practically  proved  by  certain  facts,  it  is  per- 
fectly possible  to  predict  what  sort  of  life  would  be 
found.  If  the  islands  in  question  were  so  related  to 
the  mainland  by  winds  and  currents,  that  animals 
could  very  readily  reach  them,  their  fauna  and  flora 
would  be  expected  to  be  practically  the  same  as 
those  of  the  neighboring  continent,  except  in  the 
absence  of  animals  which  could  not  cross  the  water. 
The  species  of  the  island  should  be  all  represented 
by  those  on  the  mainland.  But  when  the  island  is 
so  situated  that  it  cannot  be  visited  except  in  rare 
instances,  the  case  will  be  very  different.  Here  the 
few  animals  and  plants  which  occasionally  reach  the 
island  will  be  practically  isolated  from  their  relatives, 
the  completeness  of  the  isolation  depending  upon 
the  frequency  of  immigration  of  animals  from  the 
mainland.  Now  there  is  not  the  slightest  doubt 
that  such  isolation  will  produce  a  very  great  influ- 
ence upon  the  development  of  species.  The  de- 
scendants of  these  individuals  are  removed  from 
competition  with  other  species ;  they  are  removed 
from  the  certainty  of  cross-breeding.  Under  these 
circumstances  every  variety  will  have  a  chance  to 
perpetuate  itself.  Having  little  competition  with 
other  animals,  even  the  less  favorable  varieties  will 
be  able  to  live  and  reproduce  their  kind,  and  not 
having  numerous  unmodified  individuals  to  breed 


OCEANIC  ISLANDS.  igi 

with,  these  variations  will  have  a  chance  to  develop 
rapidly.  To  understand  the  effect  of  isolation  one 
needs  only  to  call  to  mind  the  result  of  domestic 
breeding.  The  pigeons,  for  example,  have  been  in 
a  condition  of  practical  isolation  in  the  hands  of  the 
breeders,  since  the  varieties  are  mated  together. 
The  result  of  this  is  seen  in  the  great  abundance  of 
varieties  which  have  arisen.  Indeed,  so  important 
is  this  factor  of  isolation  that  one  naturalist  is  in- 
clined to  believe  it  the  all-important  factor,  and  to 
explain  the  origin  of  every  species  by  the  isolation 
of  a  few  individuals.  Now  the  isolation  of  species 
upon  oceanic  islands  is  by  no  means  so  complete  as 
it  is  in  the  case  of  the  pigeons,  for  new  individuals 
may  from  time  to  time  arrive ;  and,  moreover,  each 
variety  which  arises  from  the  first  immigrants  is  not 
separated  by  itself.  Still  it  is  complete  enough  to 
enable  varieties  to  develop  in  a  manner  impossible 
on  the  mainland,  where  they  are  subject  to  severe 
competition.  We  may  expect,  therefore,  that  the 
species  which  arrive  upon  these  islands  will  become 
rapidly  modified,  and  soon  be  so  changed  as  to  de- 
serve the  rank  of  new  species,  assuming,  of  course, 
that  species  can  thus  arise  by  accumulation  of  varia- 
tions. And  these  species  will  further  be  closely 
related  to  those  on  the  mainland.  The  extent  to 
which  these  new  species  are  developed  will  depend 
on  the  completeness  of  the  isolation  and  the  an- 
tiquity of  the  island.  If  time  enough  is  allowed  we 
may  find  new  genera  or,  in  extreme  cases,  new  fami- 
lies. Imagine,  for  instance,  a  single  pair  of  indi- 
viduals thus  introduced  into  an  island  far  from  the 


192  EVOLUTION  OF  TO-DAY. 

continents.  Their  offspring  would  develop  varieties, 
and  by  continued  modification  these  varieties  would 
become  species,  and  the  whole  would  thus  form  a 
new  genus.  Still  later  even  greater  would  be  the 
differences.  All  of  the  new  species  thus  developed 
would,  of  course,  be  well  enough  adapted  to  the 
conditions  of  the  island,  but  utterly  unfit  to  con- 
tend in  a  struggle  for  existence  on  the  mainland. 
Nor,  indeed,  could  they  contend  with  the  species  of 
the  mainland  should  they  be  introduced  into  the 
island,  since  the  continental  species  have  developed 
under  severer  competition  and  are  consequently  the 
best  of  the  many  varieties  which  have  appeared,  all 
inferior  varieties  being  exterminated  on  the  main- 
land ;  but  this  has  not  occurred  in  islands. 

The  explanation  of  island  life  as  here  given  has 
been  the  result  of  long  study.  It  has  been  given 
here,  however,  in  order  to  make  more  intelligible  a 
few  examples.  I  have  selected  three  groups  of 
islands  to  serve  as  illustrations  of  the  principles  here 
involved,  which  form  a  series  showing  very  prettily 
that  the  above  explanations  are  correct.  The  first  is 
the  group  of  Bermudas,  situated  some  five  hundred 
miles  off  the  coast  of  North  America.  These  islands 
are  in  the  stormy  Atlantic,  and  are  subjected  to 
frequent  winds,  making  every  thing  favorable  for 
the  visiting  of  the  islands  by  birds  and  insects  and 
the  consequent  arrival  of  various  plants — for  birds 
carry  many  seeds  in  their  toes  and  crops.  Direct 
observation  proves  that  these  islands  are  thus  fre- 
quently visited.  No  less  than  one  hundred  and 
sixty-eight  species  of  birds  are  found ;  all  of  them 


OCEANIC  ISLANDS.  1 93 

except  three  are  American  birds,  and  most  of  them 
are  known  to  be  driven  to  the  islands  every  few 
years  by  storms.  These  islands  are,  therefore,  of 
the  class  most  readily  visited  from  the  continents, 
and  the  fauna  and  flora  are  in  exact  accordance  with 
this  fact,  consisting  almost  entirely  of  continental 
species  which  can  readily  cross  the  water.  There 
are  no  mammals  except  bats  and  rats.  And,  indeed, 
mammals  are  always  absent  from  oceanic  islands, 
appearing  to  have  no  power  of  crossing  large  bodies 
of  water.  There  are  no  frogs ;  and  these  animals 
also  have  no  power  to  pass  bodies  of  salt  water. 
There  are  no  snakes,  but  one  single  lizard  is  found, 
which  is  the  only  remarkable  animal  on  the  islands. 
It  is  a  peculiar  species,  and  strange  to  say  is  consid- 
ered by  Goode  to  have  its  nearest  allies  in  Africa. 
There  are  one  hundred  and  sixty-eight  species  of 
birds,  all  but  three  being  American  species  which 
have  crossed  the  water.  The  other  three  are  Euro- 
pean species  which  have  been  introduced  from 
Europe.  Insects  are  scarce,  but  all  are  either  North 
American  or  West  Indian  species.  Of  land  Mol- 
lusca  there  are  twenty  species,  four  of  which  are 
considered  peculiar  to  the  islands.  Of  the  seven 
hundred  and  twenty  species. of  plants  five  hundred 
and  seventy  have  been  introduced  since  the  advent 
of  man.  One  hundred  and  fifty  were  native  island 
species,  and  are  either  North  American  or  West 
Indian  plants.  It  is  doubtful  whether  a  single 
species  of  plant  really  deserves  to  be  called  a  pe- 
culiar species,  although  there  are  some  half  a  dozen 
which  may  possibly  be  so  ranked.  The  whole 


1 94  E  VOL  UTION  OF  TO-DA  Y. 

fauna  and  flora  is  thus  characterized  by  being  strict- 
ly American,  and,  with  the  exception  of  two  or 
three  exceptional  species,  can  be  readily  explained 
by  the  ease  with  which  animals  and  plants  can  reach 
these  islands  during  storms  and  high  winds. 

The  second  example  we  will  notice  is  the  Gala- 
pagos islands.  They  are  situated  at  about  the  same 
distance  from  South  America  that  the  Bermudas 
are  from  North  America,  but  with  one  important 
difference.  They  are  in  the  quiet  Pacific  where  vio- 
lent storms  are  almost  unknown,  and  where  even 
strong  winds  are  of  rare  occurrence.  They  are, 
therefore,  practically  much  more  removed  from  the 
mainland  than  are  the  Bermudas.  This  is  further 
proved  by  the  fact  that  visits  from  the  continent 
are  very  rare ;  the  only  actual  cases  known  are  a  few 
water-birds.  The  isolation  is,  therefore,  much  more 
complete.  Here  as  in  the  Bermudas  there  are  no 
mammals  except  rats,  even  the  bats  not  having 
succeeded  in  reaching  the  island.  The  rats  are 
doubtless  derived  from  ships  which  have  touched 
here.  Reptiles  are,  however,  quite  abundant. 
There  are  two  tortoises,  five  lizards,  and  two  snakes. 
Just  how  these  animals  succeeded  in  crossing  the 
water  it  is  of  course  impossible  to  say.  It  is  known, 
however,  that  reptiles  do  possess  some  power  of  mi- 
gration across  the  ocean.  A  living  boa-constrictor,  for 
instance,  has  been  known  to  have  reached  St.  Vin- 
cent Island,  two  hundred  miles  from  South  America. 
That  these  Galapagos  reptiles  were  derived  from 
the  mainland,  is  plainly  indicated  by  their  close 
relationship  to  the  species  now  living  in  the  conti- 


OCEANIC  ISLANDS,  195 

nent.  Although  they  are  related  to  continental 
species,  they  are  all  of  them  distinct  from  any  found 
on  the  mainland,  some  of  them  being  so  distinct  as 
to  be  sometimes  ranked  as  different  genera.  The 
two  snakes  are  very  different  from  each  other, 
belonging  to  two  families,  and  it  is  necessary,  there- 
fore, to  assume  that  two  immigrations  of  snakes 
have  occurred  in  the  past  to  account  for  the  present 
species.  The  tortoises,  although  related  to  those 
on  the  neighboring  continent,  are  distinct  species, 
and  are  very  remarkable  animals,  having  developed 
to  an  enormous  size,  doubtless  from  the  lack  of  any 
dangerous  enemies.  Of  the  fifty-seven  species  of 
birds  thirty-eight  are  peculiar  to  the  islands,  and  of 
the  other  nineteen  all  but  one  belong  to  the  water- 
birds,  which  are  always  great  wanderers ;  and  seven 
of  the  water-birds  are  peculiar.  The  only  land  bird 
common  to  the  islands  and  the  continent  is  the 
American  rice  bird  (bobolink),  which  ranges  over  the 
whole  of  North  and  part  of  South  America.  Only 
a  few  insects  have  been  found,  most  of  which  are 
peculiar  to  the  island.  And  the  same  may  be  said 
of  the  Mollusca.  Of  three  hundred  and  thirty-two 
known  species  of  flowering  plants  one  hundred  and 
seventy-four  are  peculiar,  and  about  twenty  more 
have  been  introduced  by  man.  The  rest  are  South 
American  species.  Considering,  therefore,  the  close 
relation  of  all  these  species  to  South  American 
forms,  it  cannot  be  doubted  that  they  were  origi- 
nally derived  from  that  continent ;  and  considering 
that  they  are  very  distinct  species  from  any  on  the 
continent,  it  is  hardly  possible  to  doubt  that  they 


1 96  E  VOL  UTION  OF  TO-DA  Y. 

have  been    derived    by  descent  with    modification, 
assisted  by  the  isolated  situation  of  the  islands. 

A  still  more  interesting  case  is  that  of  St.  Helena. 
This  is  a  small  island  wholly  volcanic,  very  old,  and 
situated  more  than  eleven  hundred  miles  from  Africa 
and  eighteen  hundred  miles  from  South  America. 
Its  isolation  is  therefore  very  complete.  It  can  have 
received  only  a  few  immigrants,  but  these  few  find- 
ing the  whole  field  to  themselves  have  had  abundant 
opportunity  to  develop  ;  and  since  the  island  is  very 
old,  some  of  them  will  have  had  time  enough  to  be- 
come very  much  modified.  We  may  expect  more 
peculiar  forms  than  in  the  Galapagos  islands.  With- 
in historical  times  this  island  has  been  much  altered 
by  human  agency,  and  many  new  plants  and  animals 
have  been  introduced.  Eliminating  this  factor,  the 
fauna  and  the  flora  of  the  island  are  truly  remarkable. 
There  is  only  one  vertebrate  found — a  wading  bird 
allied  to  African  forms,  but  a  distinct  species.  The 
distance  from  the  continent  has  proved  too  great 
for  the  passage  of  all  kinds  of  vertebrates.  There  are 
no  fresh-water  animals.  Of  land  shells  a  few  species 
are  known,  more  than  half  of  which  are  extinct,  and 
the  rest  so  peculiar  as  to  have  no  very  near  relatives 
anywhere.  Of  plants  seventy-six  species  have  been 
found,  fifty  of  which  belong  to  the  island  alone,  and 
"  cannot  be  regarded  as  very  close  allies  to  any 
other  plants  at  all."  The  most  interesting  group 
of  all  is  the  order  of  beetles.  There  are  one  hundred 
and  twenty-nine  species  of  beetles,  all  but  one  of 
them  found  nowhere  else  on  the  globe.  But  this  is 
not  all ;  for  while  the  specific  peculiarity  is  greater 


OCEANIC  ISLANDS.  1 97 

than  anywhere  else,  the  generic  isolation  is  equally 
remarkable.  Of  the  thirty-nine  genera  twenty-five 
are  peculiar  to  the  island,  and  many  of  them  such 
isolated  forms  that  it  is  impossible  to  find  their 
allies  in  any  particular  country.  Even  more  re- 
markable is  the  fact  that  more  than  two  thirds  of 
the  whole  number  of  species  belong  to  one  group 
(Rhyncophora),  beetles,  which  being  wood-borers 
might  readily  be  transported  on  floating  timber 
for  enormous  distances.  More  than  two  fifths  be- 
long to  one  family.  Of  the  twenty  genera  of  Rhyn- 
cophora every  one  is  peculiar  to  the  island,  and 
many  have  no  near  allies  anywhere  else  in  the  world. 
If  possible,  still  more  interesting  is  the  fact  that  all 
of  these  beetles  are  grouped  around  a  few  centres, 
as  if  they  had  only  a  few  points  of  origin.  If  seven 
or  eight  beetles  are  assumed  to  have  reached  the 
island  and  to  have  given  rise  to  varieties  which  later 
became  species,  this  peculiar  fauna  is  explained. 
The  whole  of  this  St.  Helena  fauna  is  thus  exactly 
in  accordance  with  the  extreme  age  of  the  island 
and  its  great  distance  from  the  mainlands.  It  is  an 
island  so  isolated  that  one  bird,  a  few  mollusks, 
eight  or  ten  individual  beetles,  and  a  few  plants  or 
reeds,  have  succeeded  in  reaching  it  and  establish- 
ing themselves.  Those  which  did  reach  the  island, 
however,  found  such  favorable  conditions  that  they 
rapidly  multiplied,  and  soon  gave  rise  to  numerous 
species,  all  arranged  around  several  centres,  which 
centres  represent  the  original  immigrants. 

The  significance    of   the  life  on  these  islands  is 
made    stronger   when   we    come   to  consider  other 


198  E  VOL  UTION  OF  TO-DA  Y. 

islands  which  were  once  attached  to  the  mainland, 
though  now  widely  separated  from  it.  In  these 
islands  we  have  practically  the  same  conditions 
which  are  found  in  true  oceanic  islands  with  one 
exception.  During  the  time  that  these  tracts  of 
land  were  attached  to  the  continents  they  could 
have  readily  been  supplied  with  quite  an  abundant 
fauna,  the  larger  mammals  having,  of  course,  free 
access  to  them.  When,  therefore,  they  were  finally 
separated  from  the  land,  it  would  usually  happen 
that  they  would  contain  mammals  and  other  ani- 
mals which  are  unable  to  cross  the  water.  Such 
islands  are  found  almost  always  to  contain  mam- 
mals, though  usually  they  are  distinct  species  from 
those  on  the  land.  This  fact  wellnigh  proves  that 
islands  are  peopled  from  the  continents.  Upon  any 
other  supposition  what  possible  reason  can  be  given 
why  such  islands  should  have  their  own  mammals, 
while  true  oceanic  islands  are  universally  without 
them  ?  We  thus  see  that  Australia  is  to  be  regarded 
as  such  a  fragment  of  the  continents,  which  was 
separated  from  Asia  before  true  mammals  appeared, 
and  contains,  therefore,  no  true  mammals. 

The  examples  given  above  form  no  exceptional 
cases,  for  they  only  serve  to  illustrate  the  universal 
law  regulating  island  life.  It  was  by  the  study  of 
hundreds  of  islands  in  all  sorts  of  situations  that 
such  a  law  was  clearly  shown  ;  but  island  life  every- 
where bears  out  the  above  conclusions.  Consjder- 
ing  all  cases  together,  it  has  been  abundantly  shown 
that  the  likeness  of  species  on  islands  to  those  on 
the  mainland  depends  :  (i)  upon  the  former  con- 


OCEANIC  ISLANDS.  199 

nection  of  the  land  with  the  continent,  or  the  lack 
of  such  connection  ;  (2)  upon  their  distance  from 
the  mainland  ;  (3)  upon  the  prevalence  of  winds 
and  currents  to  assist  in  immigration  of  individuals; 
and  (4)  upon  the  antiquity  of  the  island.  The 
significance  of  these  facts  is  plain. 

It  must  not  be  supposed,  however,  that  the  life  of 
oceanic  islands  offers  no  puzzling  problems,  for 
some  cases  occur  where  explanation  is  not  yet 
found.  We  occasionally  find  upon  oceanic  islands 
species  not  related  to  the  nearest  mainland,  but  to 
more  distant  countries.  The  Bermuda  lizard  has 
its  nearest  ally  in  Africa,  and  three  of  the  Bermuda 
birds  are  European  species.  The  land  shells  of  St. 
Helena  are  European  in  their  affinities.  Again,  it  is 
surprising  to  find  that  the  different  islands  of  the 
same  group  may  have  different  species.  The  Gala- 
pagos islands,  for  instance,  do  not  have  a  uniform 
fauna  and  flora,  many  species  being  confined  to 
separate  islands  only  a  few  miles  from  each  other. 
It  would  seem  that  a  few  miles  of  the  calm  Pacific 
served  as  a  more  effectual  barrier  to  prevent  the 
crossing  of  individuals  than  the  five  hundred  miles 
of  stormy  sea  which  separate  the  Bermudas  from 
the  continent.  It  has  indeed  been  shown  that 
in  the  Malayan  Archipelago  such  narrow  straits 
have  the  effect  of  practical  barriers.  A  body  of 
water  of  fifteen  miles  in  width  between  Bali  and 
Loudock  separates  effectually  two  radically  distinct 
faunas,  one  belonging  to  Asia  and  the  other  to 
Australia. 


2OO  EVOLUTION  OF  TO-DAY. 

Summary. 

The  present  distribution  of  animals  over  the  world 
is  the  result  of  countless  interacting  factors  both 
present  and  past.  The  present  distribution  is  the 
outcome  of  the  past,  and  the  former  cannot  be  un- 
derstood without  the  latter.  But  unfortunately  our 
knowledge  is  largely  confined  to  the  present,  for  the 
past  distribution  of  species  is  almost  unknown. 
Fossils  only  serve  to  give  us  occasional  glimpses  of 
the  past,  enough  to  make  possible  a  fragmentary 
history  of  the  general  past  history,  but  of  the 
origin  and  distribution  of  species  almost  nothing  is 
definitely  known.  In  the  past  as  in  the  present 
have  occurred  migrations  to  and  fro  in  search  of 
food ;  some  of  which  we  can  get  a  few  hints 
of,  while  others  are  absolutely  unknown.  All 
agencies  operating  to-day,  with  the  exception  of  the 
influence  of  man,  must  have  had  equal  force  in  the 
past.  Every  thing  combines  to  make  the  subject 
one  of  the  greatest  complexity,  and  to  confine  our 
observations  to  general  statements. 

Such  general  conclusions  in  reference  to  past 
distribution  as  can  be  made,  give  great  assistance 
in  interpreting  the  present,  and  make  it  possible  to 
create  a  science  of  the  subject  of  geographical  dis- 
tribution. When  the  past  history  of  a  group  can  be 
read  with  any  approximation  to  exactness,  its  pres- 
ent habitat  becomes  intelligible  ;  and  it  is  even  pos- 
sible to  make  predictions  as  to  the  future  discovery 
of  fossils  in  definite  localities.  The  fact  that  during 
all  of  their  past  migrations  the  species  have  been 
constantly  changing,  indicates  that  we  are  dealing 


SUMMARY.  201 

with  large  families  of  genetically  related  species.  It 
has  appeared  that,  as  a  rule,  anatomical  relationship 
is  parallel  with  geographical  relationship:  allied 
species  inhabit  contiguous  areas,  allied  genera 
usually  follow  the  same  rule ;  while  families  and 
orders  from  their  extreme  antiquity  have  almost 
always  lost  all  traces  of  this  relation  ;  that  species, 
genera,  families,  and  orders  have  had  each  a  central 
point  of  origin  ;  and  that  each  has  spread  from  this 
central  point  over  a  greater  or  less  territory,  depend- 
ing on  the  length  of  time  since  the  common  union, 
and  upon  the  powers  of  migration  which  the  animals 
in  question  possess.  All  of  this,  it  is  hardly  neces- 
sary to  say,  is  in  harmony  with  evolution.  It  is  cer- 
tainly not  out  of  harmony  with  the  idea  of  special 
creation,  which  might  also  assume  that  each  species 
has  arisen  from  a  single  pair.  But  it  is  difficult  to 
see  how  any  theory  but  that  of  descent  would  ex- 
plain the  unitary  origin  of  genera,  families,  and  or- 
ders, all  of  which  are  with  about  equal  force  traced 
back  to  a  common  point  of  origin.  Geographical 
distribution  is  in  harmony  with  evolution,  and  the 
fauna  of  oceanic  islands  very  strongly  indicate  the 
derivative  origin  of  species.  But  this  is  all  that  this 
source  of  evidence  proves,  for  it  could  not  possibly 
be  out  of  harmony  with  the  idea  of  special  creation. 
It  remains  to  be  pointed  out,  that  although  at  pres- 
ent the  subject  of  geographical  distribution  is  capable 
of  being  made  into  a  science,  with  definite  laws,  this 
possibility  is  disappearing.  The  influence  of  man 
constantly  tends  to  destroy  all  of  the  relations  above 
deduced.  Man  is  transporting  inhabitants  from  one 


2O2 


EVOLUTION  OF  TO-DAY. 


country  to  another.  Australia  and  America  are 
becoming  filled  with  European  species,  and  Europe 
is  also  receiving  many  American  forms.  Barriers  no 
longer  exist,  and  it  will  require  only  a  few  more  cen- 
turies to  modify  the  distribution  of  animals  to  such 
an  extent  that  the  rules  which  are  now  found  will 
have  more  exceptions  than  cases  of  agreement. 


CHAPTER  VI. 
DARWIN'S  EXPLANATION  OF  EVOLUTION. 

Summary  of  the  Evidence. 

WE  have  now  considered  the  chief  sources  of 
direct  evidence  which  have  been  brought  forward  in 
favor  of  organic  evolution,  as  the  result  of  many 
years'  investigation.  It  remains  to  consider  the 
various  scientific  theories  which  have  been  advanced 
to  explain  evolution.  Before  proceeding  to  this 
subject,  it  will  be  well  to  notice  what  has  been 
proved  by  the  evidence  already  deduced,  and  what 
inferences  can  be  legitimately  drawn.  It  will  in  the 
first  place  be  acknowledged  that  nothing  has  been 
positively  proved  as  to  the  question  at  issue,  for 
from  its  very  nature  evolution  is  beyond  proof. 
But  while  no  demonstration  is  possible,  the  evidence 
gradually  accumulated  has  seemed  so  strong  to 
scientists  that  it  has  led  to  an  almost  universal 
acceptance  of  evolution  in  some  form.  We  have 
seen  that  the  amount  of  variation  possible  in  any 
species  is  undoubtedly  very  great,  and,  so  far  as  can 
be  discovered,  it  is  practically  unlimited ;  that 
species  and  varieties  merge  into  each  other  in  such 
a  way  as  to  be  undistinguishable  ;  that  the  only 
definition  ever  given  of  a  species  breaks  down,  since 
203 


204  EVOLUTION  OF  TO-DAY. 

hybrids  are  not  universally  sterile,  although  they 
usually  are  so  in  animals,  but  the  presence  of  a  few 
exceptions  is  sufficient  to  show  that  there  is  no 
rigid  law  separating  species.  We  have  seen  that 
the  study  of  the  animal  kingdom  reveals  the  fact  of 
some  fundamental  bond  of  union  uniting  the  whole 
together.  This  unity  is  shown  by  the  possibility  of 
a  classification  which  is  not  artificial  but  natural, 
since  actual  relations  between  species  are  manifested 
in  the  organic  world.  This  unitary  principle  is  shown 
by  the  past  history  of  the  world  as  revealed  by 
fossils.  There  has  been  from  the  earliest  times  a 
progression  always  manifesting  itself.  All  the  fossils 
of  the  earlier  times  are  such  as  belong  to  the  same 
types  now  existing,  and  many  of  them  fall  into 
gaps  between  existing  species,  making  the  whole 
history  such  as  would  have  resulted  from  gradual 
growth.  It  is  shown  most  forcibly  of  all  by  the 
fact  that  each  individual  of  to-day  in  developing 
from  the  egg  repeats  more  or  less  exactly  the  past 
history  of  its  race  as  taught  by  fossils  and  such 
other  sources  of  evidence  as  are  at  hand.  We  have 
seen  that  for  this  universal  bond  of  union  only  two 
explanations  have  been  offered.  The  first  places  it 
in  the  mind  of  the  Creator,  and  leads  to  the  theory 
of  types.  This  theory  when  examined  has  been 
found  so  untenable  in  itself  as  to  lead  to  its  entire 
abandonment.  The  second  explanation  discovers 
the  bond  of  union  in  heredity.  This  theory  has 
been  found  to  raise  objections  of  its  own,  some  of 
which  are  of  no  little  importance.  Most  of  these 
difficulties,  however,  are  plainly  due  to  a  lack  of 


SUMMARY  OF  THE  EVIDENCE.  2O$ 

evidence,  and  contain  no  contradictions.  Some  of 
them  on  the  other  hand,  such  as  those  considered 
under  the  head  of  homology,  are  not  due  to  lack  of 
evidence,  but  indicate  that  there  are  certain  internal 
principles  of  life  which  we  do  not  understand,  and 
which  are  not  covered  by  the  heredity  explanation, 
at  least  in  its  ordinary  sense.  But  in  spite  of  these 
obstacles  the  heredity  explanation  is  the  only  one 
which  has  stood  the  test  of  examination,  and  it 
stands  more  firmly  to-day  than  ever  before.  Finally 
we  have  seen  that  the  present  distribution  of 
animals  and  plants  is  such  as  not  only  to  be  in 
accordance  with  the  descent  theory,  but  in  some 
cases  practically  to  prove  the  origin  of  species  from 
older  ones.  Specialists,  in  all  of  the  branches  of 
study  which  we  have  considered,  tell  us  that  their 
department  of  science  considers  the  question  of 
evolution  as  no  longer  questionable. 

All  of  the  evidence  is  indirect  evidence,  evolution 
being  simply  an  induction  from  the  numerous  facts. 
Granting  evolution,  and  it  is  plain  that  the  present 
condition  of  the  world  would  be  explanable  by  cer- 
tain laws.  The  study  of  the  present,  which  is  all  that 
we  have  to  study,  shows  that  the  condition  of  the 
organic  world  is  such  as  fully  coincides  with  the 
necessities  of  the  theory.  But  this  fact  does  not 
prove  the  theory  to  be  true.  Proof  is  something 
never  found  in  the  inductive  sciences,  and  the  evi- 
dence collected  here  is  of  the  same  kind  and  nearly 
as  cogent  as  that  brought  forward  for  other  induc- 
tive conclusions.  It  is,  for  example,  impossible  to 
prove  that  the  fossils  in  our  rocks  have  ever  been 


206  EVOLUTION  OF  TO-DAY. 

living  animals ;  and  it  has  been  claimed,  not  many 
centuries  ago,  that  they  did  not  represent  animal 
remains.  It  has  never  been  proved  that  our  fossils 
were  ever  alive,  and  it  is  to-day  as  possible  as 
ever  to  claim  that  they  were  put  in  the  rocks  by  the 
Creator  in  order  to  deceive  men.  But  the  good 
sense  of  the  world  has  long  since  caused  this  claim 
to  be  given  up.  And  so  in  regard  to  the  question 
we  are  considering ;  although  the  evidence  is  such 
as  would  follow  from  evolution,  and  although  all 
classes  of  facts  are  readily  explained  by  it,  the  claim 
can  still  be  made  that  the  evidence  is  in  harmony 
with  the  theory,  but  does  not  prove  it.  It  is  hardly 
possible  to  avoid  the  conclusion  that  the  good  sense 
of  the  world  will  soon  give  up  this  claim  completely, 
as  has  already  been  almost  universally  done. 

It  must  be  noticed  again,  that  if  this  evidence  is 
admitted  at  all,  it  applies  to  the  whole  animal  king- 
dom. It  is  not  possible  to  say  that  evolution  ac- 
counts for  some  species  and  not  for  all.  The  evi- 
dence is  such  that  it  must  be  extended  to  the  whole 
organic  world  or  rejected  altogether.  It  is  possible 
that  there  might  have  been  several  points  of  origin 
instead  of  one,  but  there  is  not  the  slightest  evi- 
dence that  such  was  the  case.  The  same  argument 
which  indicates  that  species  are  descended  from 
each  other,  applies  with  equal  force  to  the  origin  of 
genera,  families,  orders,  sub-kingdoms,  and  even  to  the 
two  kingdoms  of  plants  and  animals.  If  evolution  be 
admitted  in  one  place  from  the  evidence,  we  cannot 
in  honesty  deny  it  in  any  case  where  the  evidence  is 
found.  It  is  true  that  a  very  few  scientists  have 


SUMMARY  OF  THE  EVIDENCE.  -  2O/ 

held  that  there  have  been  several  starting-points  of 
origin  instead  of  one,  but  this  view  is  not  called  for 
by  the  facts,  and  is  really  of  no  value. 

While  the  various  lines  of  investigation  which  we 
have  considered  indicate  strongly  the  fact  of  genetic 
descent,  it  is  evident  that  thus  far  we  have  seen  no 
indication  of  the  manner  in  which  this  evolution  has 
been  manifested.  It  is  consistent  with  the  evidence 
we  have  considered  to  believe  that  the  evolution  of 
species  has  always  been,  as  it  seems  to  be  to-day,  an 
exceedingly  slow  process ;  that  individual  varia- 
tions have  gradually  given  rise  to  varieties,  and 
these  have  slowly  become  species,  each  species  thus 
taking  thousands  of  years  in  its  formation.  But  it 
is  also  consistent  with  the  evidence  to  believe  that 
there  have  been  periods  of  rapid  advance  and  modi- 
fication, alternated  with  periods  of  comparative  rest; 
the  present  time  being  one  of  the  latter.  It  is  pos- 
sible that  species  have  always  been  evolved  by  an 
infinite  number  of  minute  steps,  so  that  the  whole 
may  be  looked  at  as  a  .continued  growth ;  or,  it  is 
possible  that  there  may  have  been  some  abrupt  ad- 
vances, by  variations  of  considerable  amount  taking 
place  in  a  single  generation  ;  or,  it  is  even  possible 
that  these  jumps  may  have  been  great  enough  to 
originate  a  new  species  at  a  single  birth.  It  is  pos- 
sible that  evolution  may  have  been  from  the  first  a 
continued  advance,  or  there  may  have  been  at  times 
an  advance,  at  times  a  pause,'  and  at  times  a  retro- 
gression. All  of  these  conceptions  are  logical,  and 
each  has  been  and  is  held  to-day  by  various  natural- 
ists, as  expressing  in  their  opinion  the  nearest  ap- 


208  EVOLUTION  OF  TO-DAY. 

proximation  to  the  truth.     We  naturally  proceed 
first  to  the  consideration  of  the  theory  of  Darwin. 

Darwinism. 

Darwinism  and  evolution  are  often  considered  as 
synonymous  terms,  but  this  is  by  no  means  true. 
Darwin's  contribution  to  science  was  the  principle 
of  Natural  Selection.  Evolution,  as  a  theory,  had 
existed  before,  but  by  this  principle  Darwin  offered 
to  place  the  theory  on  a  firm  basis,  by  showing  the 
laws  regulating  the  production  of  species.  He  ad- 
vanced an  explanation  for  evolution.  He  "  showed 
the  possibility  of  discovering  the  path  which  Nature 
struck  out  in  order  to  produce  her  endless  variety 
of  animal  forms,  and  of  detecting  the  means  she  has 
employed  in  her  task."  He  first  showed  that  evolu- 
tion might  be  made  a  simple  theory,  founded  upon 
the  working  of  known  natural  law.  His  own  explan- 
ation may  or  may  not  be  true,  without  affecting 
materially  the  real  question.  While  evolution  is 
everywhere  accepted,  Darwinism  proper  is  largely 
given  up. 

Darwin's  explanation  of  the  method  by  which 
species  arise  from  others,  is  by  a  law  which  he  calls 
Natural  Selection,  and  which  is  called  by  Spencer 
the  Survival  of  the  Fittest.  This  law  is  so  well 
understood  by  every  one,  that  only  a  brief  summary 
is  here  necessary.  It  is,  in  general,  an  attempt  to 
explain  how  the  various  organs  of  plants  and  ani- 
mals have  become  so  admirably  adapted  to  their 
conditions,  (i)  Darwin  shows  that  animals  have  a 
tendency  to  vary.  Child  is  not  always  like  parent, 


DARWINISM.  209 

but  always  presents  some  points  of  difference.  This 
claim  has  been  abundantly  proved  and  universally 
acknowledged,  both  in  regard  to  domestic  varieties 
and  animals  under  nature.  (2)  Darwin  emphasizes 
the  old  idea  that  animals  and  plants  multiply  with 
much  greater  rapidity  than  the  food  upon  which 
they  live.  Many  more  animals  are  born  than  can 
possibly  succeed  in  reaching  maturity.  A  single 
codfish,  for  instance,  produces  some  9,000,000  eggs 
in  a  season  ;  and  if  all  reached  the  adult  state  and 
reproduced  in  like  manner,  a  very  short  time  would 
serve  to  fill  the  ocean  completely  with  codfish.  A 
vast  majority  of  the  animals  which  are  brought  into 
the  world  must  therefore  be  killed  before  reaching 
the  adult  stage.  Owing  to  this  constant  over-pro- 
duction of  young  in  every  species,  all  animals  are 
in  a  contest  with  each  other,  either  directly  or  in- 
directly, for  the  food  which  is  to  be  had.  Every 
individual  is,  therefore,  constantly  engaged  in  a 
struggle  for  existence,  and  if  he  be  weak  and  unable 
to  contend  with  others,  he  will  succumb  in  the 
struggle  and  die  before  reaching  a  condition  to 
reproduce.  (3)  This  struggle  for  existence  is  con- 
stantly affecting  all  animals,  and  it  is  evident  that 
it  is  only  the  stronger  individuals,  or  those  especially 
favored  by  some  advantage,  which  will  come  off 
victors  in  this  struggle,  and  reach  maturity  so  that 
they  can  leave  offspring.  If  some  individual  has 
an  advantage  over  others,  it  is  plain  that  it  would 
survive  and  leave  offspring.  If,  therefore,  in  the 
infinite  variations  which  are  presented  by  all  ani- 
mals, as  shown  above,  any  individual  chance  to  pos- 


210  EVOLUTION  OF  TO-DA  F. 

sess  a  variation  which  gives  it  some  special  advan- 
tage for  obtaining  food  or  fighting  with  its  enemies, 
this  individual  will  have  a  much  better  chance  than 
others  for  reaching  maturity  and  leaving  offspring. 
The  animals  best  fitted  to  the  conditions  will  sur- 
vive, while  others  will  perish.  This  is  natural  selec- 
tion. (4)  It  is  an  unquestioned  law,  that  animals 
transmit  to  their  offspring  their  own  characteristics, 
and,  therefore,  the  individuals  naturally  selected  by 
means  of  these  favorable  variations  will  transmit 
these  same  variations,  and,  as  a  result,  we  should 
find  that  nearly  all  of  the  next  generation  would 
possess  the  advantages  of  their  parents.  During  the 
succeeding  generations,  the  same  selection  will  be 
enforced,  so  that  shortly  all  of  the  -unfavored  indi- 
viduals will  disappear.  As  this  process  of  selection 
goes  on,  the  peculiarities  which  give  advantage  will 
become  more  and  more  prominent,  and  thus  a  new 
variety  of  the  old  species  will  arise,  which,  still  later, 
will  become  more  marked,  and  finally  will  be  a  new 
species. 

In  order  to  explain  the  differences  which  are  fre- 
quently found  in  the  two  sexes,  Darwin  supplements 
natural  selection  with  another  principle  which  he 
calls  Sexual  Selection.  He  shows  that  among  many 
animals  there  is  a  contest  during  the  breeding  season 
among  the  males  for  the  possession  of  the  females, 
a  contest  sometimes  by  actual  combats,  and  some- 
times by  an  attempt  to  attract  the  favor  of  the 
females  by  the  display  of  brilliant  plumage,  or  by 
singing.  In  all  of  these  cases  the  victor  in  the 
contest  mates  with  the  more  vigorous  females,  and 


DARWINISM.  211 

will  consequently  be  likely  to  leave  numerous  off- 
spring. Now,  evidently  those  males  which  have 
especially  developed  weapons  for  combat,  or  espe- 
cially beautiful  plumage,  will  be  the  victors,  and 
will  leave  the  most  vigorous  offspring ;  and  the 
offspring  will  all  have  a  tendency  to  inherit  the  same 
highly  developed  weapons  or  plumage.  This  pro- 
cess bring  repeated,  the  males  eventually  develop 
organs  like  the  antlers  of  the  male  deer,  or  the 
beauty  of  male  birds.  Occasionally  also  these  feat- 
ures are  acquired  in  a  less  marked  degree  by  the 
females  also,  since  each  sex  has  a  certain  tendency 
to  inherit  from  the  other  sex. 

By  means  of  these  two  principles,  Darwin  has  at- 
tempted to  account  for  the  origin  of  new  species 
from  the  old  upon  purely  physical  laws,  easily  un- 
derstood ;  for  evidently  if  peculiarities  can  thus  be 
accumulated  and  increased,  generation  after  gener- 
ation, the  final  result  will  be  new  animals  very 
different  from  the  old  ones.  The  strong  point  of 
this  explanation  is  its  simplicity.  It  is  based  upon 
universally  admitted  facts,  and  is  readily  understood. 
As  soon  as  the  "  Origin  of  Species  "  made  its  appear- 
ance, it  became  evident  that  Darwin  and  Wallace, 
who  had  arrived  at  the  same  principle  indepen- 
dently, had  discovered  an  important  principle,  and 
the  ready  explanation  which  natural  selection  offered 
to  large  classes  of  facts,  led  almost  immediately  to 
its  wide  acceptance.  Evolution  was  no  longer  a 
vague  hypothesis  which  added  nothing  to  knowl- 
edge, but  a  logical  theory  with  an  intelligible  ex- 
planation. Natural  selection  was  recognized  as  one 


212  E  VOL  UTION  OF  TO-DA  Y. 

of  the  laws  governing  living  things,  and  at  first 
sight  there  seemed  to  be  no  limit  to  its  action, 
which  seemed  to  lead  directly  to  evolution.  Dar- 
win obtained  at  once  prominent  followers,  who  ac- 
cepted his  theories.  Much  opposition  was,  of  course, 
aroused  among  those  who,  for  various  reasons,  did 
not  wish  to  give  up  the  idea  of  the  miraculous  in  the 
special  creation  of  species.  Among  scientists,  how- 
ever, it  was  at  first  thought  that  the  true  explanation 
had  been  found.  But  before  a  great  while  objections 
began  to  appear  from  the  world  of  science,  which 
indicated  that  natural  selection  was  not  so  complete 
an  explanation  as  it  at  first  seemed.  These  objec- 
tions have,  with  further  study,  increased  rather  than 
diminished,  until  their  accumulated  weight  has  led 
all  but  two  or  three  scientists  to  acknowledge  the 
insufficiency  of  Darwinism.  Indeed,  Darwin  him- 
self did  not  claim  to  have  found  a  complete  expla- 
nation, and  recognized  the  difficulties  of  his  theory 
even  more  forcibly  than  did  some  of  his  followers. 
In  his  later  works  he  did  not  hesitate  to  acknowl- 
edge that  he  had  at  first  overrated  its  effects,  al- 
though he  still  held  it  to  be  the  most  important 
law  regulating  the  modification  of  animals  and  the 
development  of  species.  To-day  most  naturalists, 
while  acknowledging  that  natural  selection  is  an 
important  factor,  would  give  it  a  secondary  posi- 
tion, or  at  least  modify  it  greatly  before  accepting 
it.  We  will  now  consider  the  chief  reasons  which 
have  led  to  this  conclusion. 


THE  INCOMPLETENESS  OF  DARWINISM.     21$ 

The  Incompleteness  of  Darwinism. 

It  will  be  noticed,  in  the  first  place,  that  there  are 
two  factors  in  this  theory  which  are  simply  taken  as 
facts,  without  themselves  being  explained.  The 
whole  theory  is  based  upon  the  fact  that  animals  in- 
herit the  peculiarities  of  their  parents,  but  it  gives 
no  reason  for  this  fact.  That  animals  do  transmit 
their  characteristics  to  their  offspring  is  a  fact,  but 
why  they  do  so  we  do  not  know.  Without  an 
explanation  of  this  fact,  the  mystery  of  life  remains 
as  great  as  ever.  Natural  Selection  has  nothing  to 
say  upon  this  point.  Darwin  saw  the  necessity  of 
meeting  this  factor  in  some  way  in  any  attempt  to 
discover  the  origin  of  species,  and  consequently  ad- 
vanced an  hypothesis  for  the  purpose.  A  rather 
remarkable  piece  of  pure  hypothesis  it  was,  for 
which  there  is  or  can  be  no  direct  evidence.  This 
matter  will  be  considered  more  at  length  in  the  next 
chapter. 

A  more  unfortunate  lack  in  the  Darwinian  hy- 
pothesis, is  its  failure  to  account  for  the  variations 
which  it  needs.  Natural  selection  works  entirely  by 
the  selection  of  variations,  but  is  itself  unable  to 
account  for  a  single  one.  It  can  originate  nothing. 
Given  the  variations  and  it  readily  preserves  the 
favorable  ones,  but  it  does  not  of  itself  explain  the 
appearance  of  any  thing.  Much  literature  has  been 
written  upon  the  subject  of  variation,  but  it  only 
serves  to  emphasize  our  ignorance.  Darwin  assumed 
that  animals  had  an  inherent  tendency  to  vary,  and 
thought  it  in  vain  to  attempt  to  show  the  cause  of 
any  particular  variation.  Each  variation  has  un- 


214  EVOLUTION  OF  TO-DAY. 

doubtedly  its  cause.  Changes  of  conditions  certainly 
produce  variations,  but  the  changes  of  conditions 
are  so  infinite  in  number  and  quality,  that  the  varia- 
tions which  they  produce  must  also  be  looked  upon 
as  infinite.  No  law  of  variation  has  yet  been  dis- 
covered. It  is  possible,  and  even  probable,  that 
similar  changes  in  condition  should  produce  similar 
variations  in  individuals,  but  we  can  seldom  under- 
stand why  they  should  do  so.  In  order  that  natural 
selection  can  act,  it  is  necessary  that  there  should  be 
something  to  select.  Now  we  may  concede  to  the 
theory  that  the  changes  of  conditions  are  sufficient 
to  account  for  variation.  No  two  animals  have  the 
same  surroundings,  and  we  well  know  that  the 
different  surroundings  of  animals  produce  their 
effect.  We  may  also,  for  the  present,  concede  that 
organisms  have  an  inherent  tendency  to  vary.  If 
these  two  positions  be  granted,  there  will  be  no  lack 
of  variations,  which  can  be  selected.  But  these  varia- 
tions will,  as  a  rule,  be  irregular  and  indefinite  ;  will 
be  usually  of  slight  importance,  occurring  in  any 
direction,  and  confined,  as  a  rule,  to  only  one,  or  at 
most  a  few  individuals  at  a  time.  Now  there  is  no 
doubt  that  such  variations  do  occur.  Any  one  who 
will  take  the  trouble  to  examine  a  half  a  dozen  in- 
dividuals of  any  species,  can  convince  himself  of 
this  fact.  These  variations  then,  minute,  indefinite, 
irregular,  form  the  foundation  of  Darwinism.  Such 
variations  may  be  readily  believed  to  be  due  to  the 
constantly  varying  conditions ;  and  Darwin,  per- 
ceiving them  to  be  abundant,  and  unable  to  account 
for  more  important  ones,  believed  the  natural  selec- 


DIFFICULTIES.  21$ 

tion  of  these  minute,  indefinite,  irregular,  hap- 
hazard variations  has  given  rise,  little  by  little, 
to  the  origin  and  development  of  species.  The 
question  which  naturalists  have  been  trying  to  settle 
is,  whether  selection  from  variations  of  this  charac- 
ter are  sufficient  to  produce  the.  result  ascribed  to  it. 
The  answer  which  has  been  generally  given  is  that 
natural  selection  of  chance  variations  is  not  alone 
sufficient  to  account  for  the  origin  of  species. 

Difficulties  from  the  Slowness  of  the  Modification. 

If  species  must  be  produced  by  the  selection  of 
such  minute  variations,  change  must  have  taken 
place  very  slowly,  and  the  production  of  a  new 
species  will  require  a  great  amount  of  time.  Now, 
making  all  allowance  for  error,  it  seems  to  be  almost 
certain  that  the  time  since  the  appearance  of  life  in 
the  world  has  not  been  great  enough  to  account  for 
the  development  of  the  present  species  by  any  such 
process.  The  time  since  the  Egyptian  monuments 
were  made,  which  represents  4,000-5,00x3  years,  has 
not  been  long  enough  to  produce  any  appreciable 
amount  of  change  in  domestic  species.  Even  the 
much  longer  time  since  the  glacial  period  has  had 
very  little  effect,  many  species  being  precisely  simi- 
lar to  those  of  that  time.  Darwin  estimated  that 
300,000,000  years  at  least  would  be  required  to  pro- 
duce the  present  world  of  species,  while  physicists 
will  not  admit  the  possibility  of  there  being  more 
than  100,000,000  years  since  the  world  was  inhabited, 
and  of  late  years  geologists  have  been  shortening  the 
length  of  their  geological  epochs.  Whatever  be  the 


2 1 6  E  VOL  UTION  OF  TO-DA  Y. 

length  of  this  time  in  years,  it  is  evident  enough  that 
it  has  been  sufficient  to  develop  the  present  species, 
from  the  simple  fact  that  they  have  developed  in 
this  time.  This  matter  of  time  is  no  difficulty  for 
evolution,  but  it  does  raise  an  objection  to  that  form 
of  evolution  which  evolves  species  by  the  slow  pro- 
cess of  selection  of  minute  variations.  If  change  has 
been  more  rapid  in  the  past  than  at  present,  or  if 
the  modifications  have  taken  place  by  periods  of 
rapid  advance,  alternating  with  those  of  comparative 
rest,  there  is  no  trouble  at  this  point ;  but  if  the 
slow  change  which  has  taken  place  since  the  glacial 
period  is  taken  as  a  criterion,  the  300,000,000  years 
of  Darwin  do  not  appear  to  be  a  great  demand  ;  and 
if  natural  selection  has  had  only  such  minute  varia- 
tions to  work  with  as  the  theory  assumes,  the  time 
of  the  geological  ages  appears  too  short. 

Not  only  has  this  development  of  species  been 
very  slow,  but  it  must  also  have  been  very  gradual. 
Our  present  species  have,  according  to  this  theory, 
descended  from  the  older  forms  by  slow  selection  of 
minute  variations,  which  have  always  been  in  danger 
of  disappearing  by  crossing.  There  have  been  no 
abrupt  changes.  New  species  have  not  arisen  by 
the  crossing  of  two  other  species,  but  all  have  arisen 
by  the  slow  process  of  minute  changes.  It  follows 
from  this  that  every  species  has  been  connected  with 
its  predecessor  by  a  very  great  number  of  intermedi- 
ate links,  each  varying  only  slightly  from  the  forms 
before  and  after  it.  If  we  could  get  a  comprehen- 
sive view  of  the  animals  in  the  past  and  present,  we 
would  find  no  two  species  radically  distinct,  but  all 


DIFFICULTIES.  21? 

connected  by  a  series  of  transitional  links.  It  is 
of  course  plain  that  no  such  series  of  transitional 
links  exists  to-day.  Two  closely  related  species,  in- 
habiting neighboring  localities,  are  assumed  to  have 
descended  from  a  common  ancestor,  which  has  be- 
come differently  modified  in  the  two  localities,  to 
fit  it  better  for  the  different  conditions  there  found. 
It  might  be  expected,  perhaps,  that  the  tracts  of 
land  intermediate  between  the  localities  in  question 
would  be  inhabited  by  intermediate  varieties  or 
species.  This  we  do  not,  however,  find.  The  species 
are  usually  distinct,  and,  except  in  rare  instances,  it 
does  not  happen  that  a  tract  of  land  intermediate 
between  the  localities  inhabited  by  related  species, 
is  occupied  by  an  intermediate  species,  even  though 
the  physical  condition  be  strictly  intermediate. 

The  fact  that  all  of  these  finely  graded  transitional 
varieties,  which  are  assumed  by  natural  selection  to 
have  lived  in  the  past,  no  longer  live  to-day,  pre- 
sents no  great  drfiiculty.  For  natural  selection 
and  extinction  go  hand  in  hand.  If  any  species 
be  assumed  to  have  been  derived  from  an  older 
one  by  gradual  improvement,  it  follows  that  all 
of  the  intermediate,  less-favored  varieties  must, 
by  the  action  of  natural  selection,  have  been  ex- 
terminated. The  result  will  always  be  simply  the 
preservation  of  only  the  most  advanced  forms. 
The  development  of  a  new  form  implies  the  extinc- 
tion of  the  old.  Nor  could  it  be  expected  that, 
when  two  contiguous  localities  are  inhabited  by 
related  species,  the  intermediate  tract  would  contain 
an  intermediate  species.  For  this  intermediate  tract 


21 8  EVOLUTION  OF  TO-DAY. 

will  always  be  a  comparatively  narrow  land,  and  can 
at  best  only  support  a  few  individuals,  while  the 
larger  areas  can  support  many.  We  know  that 
under  these  circumstances,  the  numerous  species 
would  replace  the  less  numerous  variety.  For  in- 
stance, if  one  species  inhabited  the  low  lands,  and 
another  the  mountains,  the  intermediate  land  will 
be  only  a  narrow  strip  at  the  base  of  the  mountains. 
It  is  evident  that  this  narrow  strip  would  not  sup- 
port a  separate  species,  but  would  rather  be  in- 
habited by  stragglers  from  the  two  species  living  on 
either  side  of  it,  and  the  two  species  would  thus 
overlap.  Thus,  it  is  easily  understood  that  inter- 
mediate forms  will  tend  to  be  exterminated. 

But  this  does  not  alter  the  fact  that  these  transi- 
tional forms  must  have  at  one  time  existed,  and 
should,  therefore,  be  found  in  the  remains  of  animals 
living  in  the  past.  We  have  already  discussed  this 
question,  and  have  seen  that  no  such  numerous 
transitional  links  exist  in  fossils.  The  reason  for 
this  has  been  found  in  the  extreme  imperfection  of 
the  geological  record.  It  is,  however,  very  ques- 
tionable whether  we  are  justified  in  considering  this 
imperfection  sufficient  to  account  for  the  almost 
utter  absence  of  these  intermediate  links.  In  one 
or  two  very  exceptional  cases  the  requisite  amount 
of  intermediate  forms  is  found,  but,  as  an  almost 
universal  rule,  this  is  not  true.  The  history  of  the 
horse  family  is  about  as  complete  as  any  history  yet 
discovered,  but  even  here  it  is  impossible  to  discover 
the  numerous  links  which  we  would  expect.  For, 
while  we  do  find  a  number  of  intermediate  stages  in 


SPECIFIC  CHARACTERS.  21$ 

the  change  from  a  five-toed  animal,  we  find  that  the 
stages  are  all  well  marked,  and  of  the  thousands  of 
transitional  forms  between  them  nothing  remains. 
It  must  have  taken  very  many  generations,  judging 
from  the  slow  modification  of  the  horse  family  to- 
day, to  have  modified  a  four-toed  animal  into  a 
three-toed  one,  and  it  is  rather  strange,  if  this 
process  did  last  such  a  long  time,  that  no  trace  of 
intermediate  forms  is  found. 

If,  in  this  case,  the  expected  links  are  wanting, 
still  more  forcibly  is  it  true  of  others  ;  for  nowhere 
is  there  found  a  fossil  history  at  all  approaching 
that  which  the  theory  would  lead  us  to  expect.  It 
is,  of  course,  impossible  to  say  whether  the  imper- 
fection of  the  record  is  sufficient  to  account  for  this 
lack.  But  it  is  certain  that  the  transition  links 
have  not  yet  been  found,  and  no  one  has  much 
hopes  that  they  ever  will  be.  This  was  a  surprise  to 
Darwin,  and  must  be  considered  as  an  objection  to 
his  theory  ;  and  it  has  also  been  a  surprise  to  others 
who  have  wished  to  follow  him  in  his  belief  in  slow, 
gradual  modification.  It  has,  moreover,  led  some 
scientists  to  a  different  view  of  the  origin  of  species, 
according  to  which  changes  have  been  rapid  and 
short,  while  periods  of  rest  have  been  very  long. 

Specific  Characters  not  always  Useful. 

A  difficulty  of  much  more  force  than  the  fore- 
going, is  one  which  emphasizes  the  fact  that  all 
variations,  in  order  that  they  be  acted  upon  by 
natural  selection,  must  be  useful.  A  useless  varia- 
tion could  never  be  selected  ;  but  it  is  demonstrable 


220  EVOLUTION  OF  TO-DAY, 

that  many  of  the  peculiarities  which  distinguish 
species  from  each  other  are  useless.  There  exist 
what  are  called  morphological  species,  by  which 
term  is  meant  species  whose  distinction  rests  upon 
some  slight  difference  in  shape,  size,  or  color — 
differences  which  can  be  of  no  use  to  the  individual. 
As  instances  of  the  point  may  be  mentioned  the 
length  of  the  ears  and  tails  of  different  rabbits  and 
mice ;  the  complex  folds  in  the  enamel  of  teeth ; 
the  peculiar  sculpturing  of  the  hair  of  different  ani- 
mals ;  the  extremely  slight  differences  in  the  mark- 
ings of  two  species,  so  slight,  frequently,  as  to  be 
distinguishable  only  with  the  closest  scrutiny ;  the 
differences  in  the  veining  of  the  wings  of  different 
butterflies,  etc.  All  such  instances  are  features  dis- 
tinguishing species,  and  must,  of  course,  be  accounted 
for  in  a  complete  explanation  of  the  origin  of 
species  ;  but,  since  they  are  of  no  use  to  their  pos- 
sessor, they  cannot,  by  any  means,  come  under  the 
influence  of  natural  selection. 

In  answer  to  such  suggestions  it  is  claimed  that 
we  never  can  say  with  positiveness  that  a  given  feat- 
ure is  of  no  use  to  its  possessor.  We  are  too  in- 
completely acquainted  with  the  lives  of  animals ; 
and  to  say  that  a  given  feature  is  of  no  use  is 
usually  an  assumption  based  on  ignorance.  This 
is  doubtless  true  ;  for  there  are  certainly  many  char- 
acteristics which  have  uses  that  we  do  not  yet 
know.  But,  on  the  other  hand,  it  must  be  remem- 
bered what  the  natural-selection  theory  means  by  a 
useful  structure.  In  order  that  a  peculiarity  should 
be  preserved  by  natural  selection,  it  must  be  of  so 


SPECIFIC  CHARACTERS.  221 

much  importance  as  to  cause  its  possessor  to  live 
under  circumstances  when  other  individuals  die  ;  or 
to  flourish  better  and  so  leave  more  offspring.  This 
fact  is  too  frequently  overlooked.  When  the  fact  of 
the  great  struggle  for  existence  is  recognized,  it  be- 
comes plain  that  those  animals  best  fitted  to  the 
struggle  will  have  the  best  chance  of  surviving  and 
of  producing  their  kind.  It  soon  becomes  imagined 
from  this  that  the  very  slightest  usefulness  in  an 
organ  is  enough  to  bring  it  under  the  powerful  influ- 
ence of  natural  selection.  But  this  can  hardly  be 
true;  for  natural  selection  acts  by  life  and  death, 
and  a  variation  must  be  of  some  considerable  im- 
portance to  cause  the  survival  of  its  possessors  and 
the  destruction  of  individuals  not  possessing  it.  It 
is  beyond  credulity  to  believe  that  the  microscopic 
sculpturings  on  the  hair  of  the  rabbit  are  of  enough 
importance  to  cause  their  perpetuation  by  selection. 
There  can  be  no  doubt,  therefore,  that  many  charac- 
teristics are  of  so  little  use  that  natural  selection 
can  have  had  no  influence  in  causing  their  develop- 
ment. It  is  difficult  enough  to  believe  that  the  com- 
plicated functional  organs  of  the  body  have  been  de- 
veloped through  countless  stages,  each  of  which  is  of 
sufficient  use  to  its  possessor  to  cause  its  exclusive 
preservation  ;  and  much  less  is  it  possible  to  con- 
ceive that  the  various  characteristics  of  the  morpho- 
logical species  were  developed  in  this  way. 

The  only  other  suggestion  for  meeting  these  cases 
is  by  what  is  called  correlated  variation.  The  organ- 
ism is  bound  together  in  such  a  way  that  when  one 
part  varies  other  parts  have  also  a  tendency  to 


222  EVOLUTION  OF  TO-DA  Y. 

change.  As  to  what  it  may  be  that  causes  cer- 
tain organs  to  be  thus  united  we  know  nothing,  but 
that  such  correlated  organs  exist  is  beyond  ques- 
tion. It  is  not  necessary,  therefore,  to  assume  that 
all  variations  must  be  useful  in  order  that  they 
be  selected,  but  only  that  they  are  connected  with 
others  which  are  useful.  It  may  be  that  many  of 
these  useless  peculiarities  are  in  this  manner  con- 
nected with  others  that  are  useful,  and  that  the  de- 
velopment of  one  implies  the  development  of  the 
other.  The  useful  variation  will  be  preserved  by 
natural  selection,  and  the  useless  variation  will 
necessarily  be  preserved  and  developed  in  a  par- 
allel manner.  Much  is  attributed  also  to  the 
laws  of  growth,  by  which  is  meant  the  obscure 
laws  which  regulate  the  flow  of  nutriment,  etc. 
Many  important  features  may  be  thus  explained. 
Some  plants  have  their  leaves  opposite  each  other, 
others  have  them  alternating ;  and  this  point,  of 
no  use  to  the  plant,  may  be  regulated  by  the  flow  of 
sap  in  the  two  cases.  But  at  best  these  two  sugges- 
tions are  of  little  assistance,  and  simply  serve  to  in- 
dicate that  there  is  an  unexplained  difficulty  here. 
That  they  do  not  sufficiently  explain  useless  feat- 
ures is  so  well  proved  that  even  Darwin  was  at  last 
inclined  to  admit  the  great  potency  of  "  spontaneous 
variation,"  and  with  this  phrase  he  abandons  all  at- 
tempt to  reach  a  clear  understanding  of  the  matter. 
Natural  selection  thus  fails  to  reach  this  large  class 
of  features,  which  are  of  no  use  to  their  possessor, 
and  does  not  help  in  understanding  the  origin  of 
species  whose  distinctions  are  founded  upon  such 
features. 


SPECIFIC  CHARACTERS,  22$ 

Quite  similar  in  their  import  are  structures  which 
are  simply  ornamental.  For  ornament  in  itself 
natural  selection  has  no  room.  To  be  selected,  a 
variation  must  be  useful.  The  only  chance  for  the 
development  of  ornament  in  the  Darwinian  hypothe- 
sis is  by  sexual  selection.  Among  some  animals, 
particularly  birds,  the  most  vigorous  females  select 
for  their  mates  the  most  beautiful  males,  and  this 
would,  of  course,  enhance  the  beauty.  But  many 
of  the  most  ornamental  structures  are  met  with 
among  animals  where  this  sort  of  selection  is  impos- 
sible. Some  mollusks  are  among  the  most  beautiful 
organisms  in  existence,  the  delicacy  of  the  tints  of 
the  shell  and  the  beauty  of  the  sculpturing  being 
exquisite  ;  but  sexual  selection  is  impossible  here, 
for  the  animals  are  mutually  hermaphrodite.  And, 
indeed,  their  sensory  organs  are  so  imperfect  that  it 
is  impossible  for  them  to  see  the  beauty  of  their 
own  shells,  to  say  nothing  of  appreciating  it.  More- 
over, many  of  them  keep  their  shell  entirely  covered 
during  life  by  the  mantle,  and  the  ornamental  feat- 
ures only  appear  after  death.  Such  features  can 
only  be  regarded  as  due  to  the  laws  of  growth,  which 
regulate  the  absorption  of  nutriment  in  such  a  man- 
ner as  to  produce  certain  results,  some  of  which 
appear  to  us  as  beautiful.  Indeed,  beauty  is  only  a 
subjective  feature,  depending  not  on  the  object,  but 
upon  the  observer.  Why  many  animals  possess 
features  which  seem  beautiful  to  us,  we  do  not 
know;  but  it  is  not  simply  for  the  sake  of  being 
beautiful,  and  it  is  equally  certain  that  it  is  not  due 
either  to  natural  or  sexual  selection. 


224  EVOLUTION  OF  TO-DAY. 

Variations  Eliminated  by  Crossing. 
A  still  more  serious  difficulty  amounts  to  a  dem- 
onstration that,  as  originally  conceived,  natural 
selection  is  not  adequate  to  explain  the  facts.  It  is 
the  tendency  of  varieties  to  disappear  by  crossing. 
A  reviewer  in  the  North  British  Review  in  1867 
demonstrated  the  necessity  of  assuming  that  varia- 
tions appear  in  many  individuals  at  once,  showing 
that  it  is  mathematically  impossible  for  a  single 
variation  to  be  preserved,  no  matter  how  valuable  it 
be.  He  takes,  for  an  example,  the  instance  of  an 
animal  which  produces  two  hundred  young,  of 
which  only  two  survive  the  struggle  for  existence 
long  enough  to  produce  young.  He  assumes  that 
one  of  the  two  hundred  has,  by  a  chance  variation, 
some  feature  not  possessed  by  the  others,  and  which 
is  highly  valuable  (it  must  be  remembered  that  vari- 
ations, as  a  rule,  are  so  slight  as  to  be  of  little  use). 
Now,  in  the  above  case,  the  chance  for  the  survival 
of  this  particular  individual  is  not  very  great. 
Doubtless  this  animal  would  have  a  better  chance  of 
survival  than  any  other  individual,  but  the  chances 
are  much  in  favor  of  some  other  of  the  two  hundred. 
This  single  individual,  while  having  superior  facili- 
ties, must  contend  with  great  numbers,  and  its 
chances  for  preservation  are  therefore  not  very  great. 
But  even  supposing  it  to  survive  and  produce 
young,  it  will,  of  course,  be  obliged  to  mate  with 
some  individual  not  possessing  its  favorable  peculi- 
arities, and  its  offspring  will  inherit  the  peculiarities 
in  a  less  marked  degree.  "  It  will  breed  and  have  a 
progeny  of,  say,  one  hundred.  Now  this  progeny 


VARIATIONS.  225 

will,  on  the  whole,  be  intermediate  between  the 
average  individual  and  the  sport.  The  odds  in 
favor  of  one  of  this  generation  will  be,  say,  one  and 
a  half  to  one,  as  compared  with  the  average  indi- 
vidual ;  the  odds  in  their  favor  will  be  less  than  that 
of  their  parent.  But,  owing  to  their  greater  number, 
the  chances  are  that  about  one  and  a  half  would 
survive.  Unless  these  breed  together,  a  most  im- 
probable event,  their  progeny  would  again  approach 
the  average  individual.  There  would  be  one  hun- 
dred and  fifty  of  them,  and  their  superiority  would 
be,  say,  in  the  ratio  of  one  and  a  quarter  to  one." 
In  the  next  generation  the  superiority  by  further 
crossing  would  be  even  less  ;  and  thus  the  variation 
which  appears  so  strong  in  the  first  individual  will 
dwindle  away,  and  in  a  few  generations  practically 
disappear.  While  natural  selection  would  have  a  ten- 
dency to  select  the  favored  individual,  the  necessity 
of  cross-breeding  would  have  a  much  more  powerful 
effect  in  causing  the  variation  to  disappear. 

To  this  difficulty  no  one  has  suggested  any  suffi- 
cient answer.  Darwin  acknowledged  its  full  force, 
and  admitted  that  very  rarely  is  it  possible  for  a 
single  variation  to  be  preserved.  He  thinks,  how- 
ever, that  if  a  third,  a  fifth,  or  even  a  tenth  part  of 
the  individuals  be  simultaneously  modified  by  some 
cause  (such  as  similar  conditions  affecting  different 
individuals  in  a  similar  way),  and  if  the  variation 
should  be  of  a  beneficial  nature,  the  original  form 
would  soon  be  supplanted  by  the  modified  form 
through  the  survival  of  the  fittest.  This  will  prob- 
ably be  admitted  by  all,  but  it  is  evident  that  with 


226  EVOLUTION  OF  TO-DAY. 

this  admission  on  Darwin's  part,  his  original  theory 
has  become  so  much  modified  that  it  is  no  longer 
simply  natural  selection.  The  fundamental  cause 
in  the  change  in  species  is  something  which  pro- 
duces simultaneous  variations.  Upon  these  varia- 
tions natural  selection  may  act,  but  it  is  secondary, 
the  primal  fact  being  the  law  or  laws  which  produce 
simultaneous  variations  in  many  individuals. 

It  must,  however,  be  noticed  that  observation 
teaches  that  crosses  between  two  varieties  do  not 
always  produce  intermediate  varieties ;  sometimes 
the  offspring  show  all  of  the  features  of  one  parent. 
When  the  Ancon  ram  is  crossed  with  the  female  of 
an  ordinary  breed,  the  young  are  of  the  Ancon  va- 
riety, and  not  an  intermediate  form. 

Development  of  Organs  by  Small  Steps. 

Not  only  has  the  necessity  of  simultaneous  varia- 
tions been  clearly  shown,  but  it  seems  equally 
evident  that  some  of  these  variations  must  be  of 
considerable  importance.  Many  organs  can  hardly 
be  explained  as  being  developed  by  small  steps, 
such  as  those  of  which  natural  selection  is  supposed 
to  make  use.  In  the  first  place,  it  is  impossible  to 
understand  how  certain  organs  could  have  origi- 
nated in  this  way,  for  they  are  of  such  a  nature  as 
to  be  of  no  use  until  highly  developed.  After  they 
get  well  enough  developed  to  be  used,  it  is  easily 
conceivable  that  they  may  be  preserved  by  natural 
selection,  and  even  further  perfected  ;  but  at  first 
they  are  useless,  and  cannot  therefore  be  selected. 
This  point  can  be  made  more  intelligible  by  an 


DEVELOPMENT  BY  SMALL   STEPS.  22? 

illustration,  and  I  select  for  this  purpose  an  exam- 
ple frequently  used — the  whalebone  in  the  mouth 
of  the  Greenland  whale.  This  organ  consists  of  a 
large  number  of  long  horny  plates,  hanging  down 
from  the  front  of  the  palate  on  either  side  of  the 
mouth.  They  form  two  longitudinal  series  of  plates 
very  close  together.  The  inner  edges  of  the  plates 
are  frayed  into  a  hair-like  fringe,  and  the  whole 
forms  a  sort  of  sieve  at  the  sides  of  the  mouth. 
When  the  whale  feeds,  he  opens  his  mouth  widely, 
taking  into  it  quantities  of  water,  together  with 
many  small  animals,  which  form  his  food  ;  and  then 
closing  his  mouth,  the  water  is  forced  out  through 
this  sieve  of  baleen  plates.  The  water  readily  passes 
through  them,  while  the  animals  are  retained  in  the 
mouth,  and  are  now  swallowed.  The  beauty  of  this 
contrivance  is  evident  at  once,  enabling  the  animal 
as  it  does  to  feed  upon  small  food  under  water. 
After  it  has  once  become  perfected  enough  to  be 
thus  used,  it  is  easy  to  see  that  natural  selection 
could  cause  its  preservation.  But  the  question  is, 
how  such  an  organ  could  have  arisen  by  small 
stages,  since  it  would  obviously  be  of  no  use  until 
the  plates  became  long  enough  to  serve  as  a  sieve ; 
and  there  must  have  been  a  very  long  time,  while 
the  organ  was  developing,  when  it  would  not  be  large 
enough  to  serve  in  this  way,  and  was  yet  preserved. 
How  such  an  organ,  or  any  similar  organ,  useful  only 
when  highly  developed,  could  have  been  started  on 
its  line  of  development  upon  this  theory,  it  is  diffi- 
cult to  see,  for  it  would  seem  that  at  first  the  vari- 
ations would  have  been  of  no  use,  and  consequently 
not  under  the  influence  of  natural  selection. 


228  EVOLUTION  OF  TO-DAY. 

Darwin  has  answered  this  objection  in  a  manner 
partially,  though  perhaps  not  wholly,  satisfactory. 
He  says  it  is  true  that  these  organs  at  the  beginning 
could  be  of  no  use  for  the  purpose  to  which  they  are 
now  applied,  but  it  is  easy  to  conceive  that  they 
might  have  been  used  for  some  other  purpose,  and 
thus  even  the  rudimentary  beginnings  might  be  of  use, 
and  hence  selected.  To  use  the  same  example,  which 
Darwin  has  also  fully  discussed,  we  may  quite  readily 
imagine  that  the  early  whale  ancestor  had  upon  the 
roof  of  its  mouth  a  few  horny  protuberances,  such 
as  are  found  in  the  mouth  of  a  goose  ;  of  no  use  for 
sifting  food,  but  aiding  in  the  seizing  and  tearing  of 
food.  They  would  be  of  use,  and  therefore  preserved 
by  natural  selection,  and  may,  therefore,  be  sup- 
posed to  develop  slowly  until  they  became  some- 
what larger.  After  they  became  of  some  consider- 
able size,  they  would  be  used  both  for  seizing  food 
and  sifting  water,  a  condition  of  things  found  in 
the  Egyptian  goose.  A  little  further  development 
would  convert  them  into  lamella,  like  those  of  the 
duck,  and  so  onwards  until  they  became  large  enough 
to  be  used  exclusively  for  sifting,  as  they  are  in  the 
shoveller  duck.  Now  these  lamella  of  the  shoveller 
duck  are  relatively  not  much  shorter  than  the  baleen 
plates  of  some  whales,  and  it  is  easy  to  see  how  the 
organs,  now  used  exclusively  as  sifting  organs,  may 
be  further  developed  by  natural  selection,  until  they 
reach  the  size  of  the  whalebone  plates.  In  this  way 
we  can  see  how  even  such  an  organ  as  the  baleen 
might  have  been  developed  by  gradual  stages,  each 
of  which  was  of  use  for  some  purpose,  though  per- 


DEVELOPMENT  BY  SMALL   STEPS.  22Q 

haps  a  constantly  changing  one, — a  change  in  func- 
tion accompanying  a  change  in  form.  In  a  similar 
manner  Darwin  has  treated  other  cases  of  this  kind 
which  have  been  suggested,  and  has  had  remarkable 
success  in  showing  that  it  is  possible  to  understand 
how  by  a  change  of  function  natural  selection  might 
extend  to  organs  seemingly  of  no  use  except  in  their 
highly  developed  condition.  His  explanations  are, 
of  course,  plainly  hypothetical.  Even  granting  them 
sufficient,  it  still  appears  that  the  very  first  beginning 
of  such  organs  is  difficult  to  account  for.  In  the 
case  given  it  may  well  be  that,  after  the  horny  pro- 
jections had  become  large  enough  and  strong  enough 
to  aid  materially  in  seizing  and  tearing  food,  they 
would  be  preserved  by  natural  selection  ;  but  the 
ordinary  variations  are  too  small  to  account  for  the 
sudden  appearance  even  of  such  protuberances.  It 
is  altogether  too  much  for  one's  credulity  to  be- 
lieve that  the  presence  of  one  or  two  accidental 
roughenings  in  the  mouths  of  one  or  two  animals 
would  be  of  enough  advantage  to  lead  to  the  survival 
of  these  individuals  and  the  extinction  of  others 
which  did  not  chance  to  possess  them.  If  we  can 
assume  that  at  some  time  in  the  past  there  was  a 
sudden  great  variation  in  the  mouths  of  the  whales' 
ancestors,  affecting  many  individuals  at  once,  the 
solution  offered  by  Darwin  may  be  accepted  ;  but 
so  long  as  it  is  only  scattered,  indefinite,  minute 
variations  which  natural  selection  has  to  work  upon, 
the  difficulty  herein  lying  is  very  great. 

But  even  after  the  beginning  of   organs    is   ac- 
counted for,  it  is  equally  difficult  to  see  how  they 


230  EVOLUTION  OF  TO-DAY. 

could  be  developed  by  the  accumulation  of  minute 
variations.  The  variations  of  animals  under  ordi- 
nary circumstances  are  very  slight,  so  slight,  indeed, 
that  only  one  long  accustomed  to  breeding  animals 
can  distinguish  them ;  yet  it  is  such  minute  varia- 
tions that  natural  selection  is  supposed  to  make  use 
of.  Darwin,  indeed,  believed  that  natural  selection 
is  much  more  exact  than  is  the  artificial  selection  of 
breeders,  picking  out  constantly  features  which  the 
eye  cannot  detect.  But  while  this  may  be  true  in 
some  cases,  it  is  hardly  possible  to  believe  that  most 
of  these  small  variations  can  be  of  enough  import- 
ance to  be  selected.  When  accumulated  they  may 
undoubtedly  be  of  importance,  but  in  order  that 
natural  selection  may  accumulate  them,  it  is  neces- 
sary that  each  one  must  be  of  so  much  importance 
as  to  lead  its  possessor  to  a  great  superiority  over 
other  animals.  To  take  one  or  two  examples : 
The  potto  (a  lemur)  has  the  peculiarity  of  having 
only  three  fingers,  the  forefinger  being  a  mere 
rudiment.  Now  whether  this  peculiarity  be  of  any 
use  to  the  animal,  it  is  impossible  to  say ;  but  grant- 
ing that  it  is  of  use,  it  must  be  assumed  that  at  one 
time  in  the  ancestors  of  the  potto  this  finger  was 
equal  in  size  to  the  others,  and  that  it  has  gradually 
diminished  in  size.  If  variations  are  minute  in  ex- 
tent, this  shortening  of  the  finger  must  have  been 
very  slow ;  and  it  is  hardly  possible  to  believe  the 
shortening  of  the  finger  by  a  slight  fraction  of  an 
inch  at  a  time  could  have  been  of  any  use  to  the 
animal,  even  though  the  completely  rudimentary 
finger  is  of  advantage.  When  we  consider  that  not 


SIMILARITY  IN  ACQUIRED   ORGANS.          2$l 

only  must  these  small  variations  be  of  use,  but  in 
order  that  they  should  be  selected,  they  must  be  of 
so  much  use  as  to  lead  the  individuals  with  this 
variation  to  flourish  in  conditions  where  other  indi- 
viduals will  have  difficulty  in  living,  and  thus  to 
cause  the  modified  variety  to  supplant  the  unmodi- 
fied form  ;  and  when,  further,  we  remember  the 
results  which  must  arise  by  crossing  of  modified  and 
unmodified  individuals,  it  is  simply  impossible  to 
believe  that  this  peculiarity  could  have  been  devel 
oped  by  the  natural  selection  of  minute  variations. 
Or,  take  the  case  of  the  development  of  the  horse's 
foot.  Granting  that  it  is  of  great  advantage  to  the 
horse  to  have  one  large  toe  rather  than  five  small 
ones,  it  is  incredible  that  any  single  ancestor,  hap- 
pening to  have  a  slightly  larger  middle  toe,  would 
so  far  surpass  all  others  that  it  should  event- 
ually supplant  the  unmodified  form.  If  we  can 
believe  that  many  horses  have  varied  simultaneously 
and  rapidly  as  regards  the  shape  of  the  toe,  it  is 
quite  easy  to  see  that  natural  selection  might  have 
developed  the  modern  horse's  foot ;  but  so  long  as 
there  are  only  indefinite  variations,  it  is  no  longer 
within  the  realm  of  possibility. 

Similarity  in  Independently  Acquired  Organs. 

Natural  selection  finds  further  difficulty  in  ex- 
plaining the  similarity  of  independently  acquired 
organs.  It  is  the  verdict  of  one  scientist  that  "  it  is  so 
improbable  as  to  be  practically  impossible  for  two 
exactly  similar  structures  to  have  ever  been  inde- 
pendently acquired."  It  is  found  that,  as  a  rule, 


232  EVOLUTION  OF  TO-DAY. 

animals  not  closely  related  do  not  possess  similar 
organs,  the  same  function  being  differently  per- 
formed. But  it  is  not  impossible  to  find  instances 
where  organs  bearing  the  greatest  similarity  are 
found  in  animals  so  distantly  related  as  to  preclude 
the  idea  of  inheritance  as  an -explanation,  and  to 
make  it  necessary  to  assume  that  they  are  indepen- 
dently acquired.  Probably  the  best  illustration  that 
can  be  selected  is  found  in  the  eye  of  the  vertebrates 
and  mollusks.  These  two  groups  of  animals  are 
very  widely  separated  from  each  other,  and  any 
organs  which  they  possess  in  common,  except  those 
found  in  all  animals,  must  have  been  independently 
acquired,  since  they  separated  from  each  other  in 
the  ancient  pre-silurian  times.  Now  the  higher 
members  of  the  mollusks  (cephalopods)  possess  eyes 
which  bear  the  greatest  similarity  to  those  of  verte- 
brates, each  having  sclerotic,  retina,  choroid,  vitreous 
humor,  aqueous  humor,  and  lens.  The  correspond- 
ence at  first  sight  seems  complete,  and  remember- 
ing the  remarkable  complexity  of  the  organ,  together 
with  the  fact  that  the  various  parts  are  only  of  use 
when  the  others  are  present,  it  becomes  a  marvellous 
thing  to  find  such  an  organ  independently  developed 
in  two  different  cases.  This  difficulty  Darwin  has 
answered  as  follows  :  "  Beyond  a  superficial  resem- 
blance, there  is  hardly  any  real  similarity  between 
the  eyes  of  cuttle-fishes  and  vertebrates.  *  *  *  The 
crystalline  lens  in  higher  cuttle-fishes  consists  of  two 
parts  placed  one  behind  the  other  like  two  lenses, 
both  having  a  very  different  structure  and  disposi- 
tion to  what  occurs  in  the  vertebrates.  The  retina 


SIMILARITY  IN  ACQUIRED   ORGANS.          233 

is  wholly  different,  with  an  actual  inversion  of  the 
elemental  parts,  and  with  a  large  nervous  ganglion 
included  within  the  membranes  of  the  eye.  The 
relations  of  muscles  are  as  different  as  it  is  possible 
to  conceive,  and  so  in  other  parts.  *  *  *  It  is 
of  course  open  to  any  one  to  deny  that  the  eye  in 
either  case  could  have  been  developed  through  nat- 
ural selection  of  successive  slight  variations,  but  if 
this  be  admitted  in  the  one  case  it  is  clearly  possible 
in  the  other ;  and  fundamental  differences  in  struc- 
ture in  the  visual  organs  might  have  been  anticipated 
in  accordance  with  this  view  of  their  formation.  As 
two  men  sometimes  independently  hit  on  the  same 
invention,  so  in  the  several  foregoing  cases  it  ap- 
pears that  natural  selection,  working  for  the  good  of 
each  being,  and  taking  advantage  of  all  favorable 
variations,  has  produced  similar  organs,  as  far  as 
function  is  concerned,  in  distinct  organic  beings 
which  owe  none  of  their  structure  in  common  to 
inheritance  from  a  common  ancestor." 

It  is  generally  admitted  that  this  answer  of  Dar- 
win is  sufficient  to  meet  the  case,  at  least  in  part. 
A  visual  organ  to  have  any  high  degree  of  efficiency 
must  possess  certain  fundamental  parts :  must  have 
a  dark  chamber,  a  spread-out  optic  nerve  or  retina, 
and  a  series  of  lenses  to  form  an  image  on  the  ret- 
ina. Beyond  these  necessary  features  there  are 
hardly  any  common  points  between  the  two  eyes. 
But  some  would  still  claim  that  the  difficulty  is  not 
met.  For  it  has  indeed  been  increased  rather  than 
diminished  by  observation  since  the  above  answer 
of  Darwin's  was  written.  Another  mollusk,  Pecten 


234  EVOLUTION  OF  TO-DAY. 

(the  scallop),  belongs  to  a  group  very  distantly  re- 
lated to  the  cuttle-fishes  ;  it  has  around  the  edge  of 
its  mantle  a  series  of  eyes,  which  can  therefore  have 
no  inherited  likeness  either  to  the  cuttle-fish  eye  or 
the  vertebrate  eye.  But  here,  too,  is  developed  the 
same  sort  of  complicated  eye  with  its  various  parts, 
and  here  the  likeness  to  the  vertebrate  eye  is  even 
more  pronunced,  the  various  coats  being  in  almost 
exactly  the  same  order  in  the  two  cases.  Since 
Pecten,the  cuttle-fishes,  and  the  vertebrates  are  very 
widely  separated  from  each  other,  we  have  in  these 
cases  three  organs  very  similar  to  each  other,  inde- 
pendently acquired.  It  is  enough  to  tax  one's 
imagination  to  believe  that  such  a  complicated 
organ  as  the  eye  could  ever  have  been  developed 
by  selection  of  minute  variation  ;  but  when  we  thus 
find  at  least  three  cases  where  quite  similar  organs 
are  independently  developed,  it  is  plain  that  we 
have  considerable  of  a  problem.  That  these  organs 
could  have  been  developed  by  chance  is  incredible, 
and  it  must  be  claimed  that  the  conditions  requisite 
for  a  visual  organ  are  so  rigid  that  all  eyes  must 
have  developed  in  this  way  in  order  to  be  of  any 
use.  Now  this  type  of  eye  is  not  the  only  type 
which  is  found,  for  Crustacea  and  insects  have  visual 
organs  made  upon  an  entirely  different  plan.  To 
make  the  matter  still  more  perplexing,  we  find  that 
some  mollusks  have  eyes  built  upon  the  plan  of  in- 
sect eyes  (Area  and  Pectunculus).  The  whole  mat- 
ter is  indeed  a  puzzle.  Unquestionably  the  same 
sort  of  eye  has  been  independently  acquired  in 
several  cases,  and  since  it  can  hardly  be  believed 


MIMICRY.  235 

that  the  external  conditions  are  so  rigid  as  to  limit 
the  visual  organs  to  one  or  two  lines,  it  would 
seem  to  be  a  warrantable  assumption  that  there  is 
some  internal  condition  which  regulates  the  struc- 
ture of  such  organs. 

Mimicry. 

Numerous  other  instances  of  independently  ac- 
quired organs  could  be  given,  but  none  so  striking 
as  the  one  mentioned  above,  while  many  of  them 
are  readily  understood  upon  purely  physical  laws. 
The  likeness  in  shape  between  the  wings  of  the  bird 
and  the  butterfly,  for  example,  is  the  result  of  the 
advantage  which  this  shape  possesses  for  an  organ 
of  flight. 

But  an  interesting  series  of  independently  ac- 
quired likenesses  must  be  mentioned,  not  because  it 
presents  any  great  difficulty,  but  rather  because  it  is 
the  best  illustration  of  the  action  of  natural  selec- 
tion. Reference  is  made  to  the  subject  of  mimicry. 
Many  animals,  particularly  insects,  possess  the  form 
and  appearance  of  other  animals  for  the  protection 
thus  afforded.  Some  flies  resemble  wasps,  and 
doubtless  many  thus  escape  destruction  by  being 
mistaken  for  the  more  dangerous  insects.  Certain 
butterflies  seem  to  be  distasteful  to  insectivorous 
birds,  and  others,  which  are  not  distasteful,  acquire 
the  same  form  as  distasteful  species,  and  thus  the 
birds  pass  them  by.  Beetles  imitate  ants  for  similar 
purposes,  and  many  animals  have  a  similar  pro- 
tective resemblance  to  inanimate  objects.  Our 
grass  snakes  are  green  ;  one  butterfly,  with  its  wings 


236  EVOLUTION  OF  TO-DAY. 

folded,  very  accurately  resembles  the  leaves  of  the 
plant  on  which  it  lives,  the  resemblance  being 
carried  even  to  the  veining  of  the  leaf  and  its 
petiole.  In  other  cases  the  likeness  may  be  carried 
to  even  a  greater  extent,  spots  appearing  on  the 
wings  resembling  injuries  caused  by  fungi  on  the 
leaf.  Or  others  may  resemble  dry  sticks,  their  legs 
stretching  out  irregularly  in  various  directions  so  as 
to  resemble  branches.  The  object  of  all  this  is  evi- 
dent enough.  It  enables  the  animals  in  question  to 
avoid  destruction.  It  is  a  clear  case  of  natural 
selection.  An  insectivorous  bird  sits  on  the  branch 
of  a  tree  and  watches  for  butterflies/  As  soon  as  it 
sees  one  flying  across  an  open  tract,  if  it  appear  to 
be  of  the  species  which  the  bird  knows,  from 
experience,  to  be  pleasant  to  the  taste,  the  bird 
leaves  its  perch,  pursues  and  captures  the  butterfly. 
If,  however,  the  butterfly  should  appear  to  be  one 
of  the  distasteful  species,  the  bird  pays  no  attention 
to  it.  If  the  tasteful  species  have  individuals  bear- 
ing slight  chance  resemblance  to  the  distasteful 
species,  these  individuals  will  be  the  ones  to  escape 
destruction  and  to  perpetuate  their  kind.  Thus  the 
beginning  of  mimicry  is  easily  understood.  As  the 
mimicking  species  becomes  more  abundant,  the 
birds  will  learn  to  look  more  sharply  before  reject- 
ing any  individual,  and  it  will  only  be  those  having 
a  very  close  mimicry  that  will  be  preserved.  As  the 
bird  becomes  wiser  and  sharper  in  its  scrutiny,  the 
mimicry  must  become  more  perfect,  and  eventually 
a  remarkable  perfection  in  mimicry  may  be  reached. 
All  this  will  result  from  the  action  of  natural  selec- 


STERILE  INSECTS.  237 

tion,  if  it  be  granted  that  the  shape,  size,  and  color- 
ing of  the  butterfly's  wings  are  variable.  It  is,  of 
course,  questioned  whether,  even  with  this  rigid 
selection,  slight,  indefinite  variations  are  enough  to 
account  for  the  final  completion  of  some  of  the 
wonderful  pieces  of  mimicry,  but  this  objection  is  so 
similar  to  one  already  discussed  that  we  need  do  no 
more  than  mention  it,  and  indicate  that  it  is  fre- 
quently regarded  as  a  very  great  difficulty  for 
natural  selection. 

Sterile  Insects. 

There  is  one  special  difficulty  to  the  principle,  of 
so  much  weight  as  to  deserve  notice  here,  although 
it  is  not  our  purpose  to  consider  special  cases.  This 
is  the  difficulty  in  seeing  how  the  working  castes  of 
various  insects  could  have  arisen,  and  it  is  so  much 
of  an  obstacle  that  Darwin  at  first  thought  it  fatal 
to  his  theory.  Many  insects,  such  as  ants  and  bees, 
live  in  large  communities,  thousands  of  them  com- 
bining to  live  in  mutual  dependence  on  each  other. 
The  labor  of  the  colony  is  divided  among  different 
members,  each  being  fitted  to  perform  certain  work. 
In  the  beehive  is  found  the  queen  bee,  who  pro- 
duces all  of  the  eggs  ;  the  drones,  whose  sole  duty 
is  to  fertilize  the  eggs  ;  and,  finally,  the  workers, 
who  take  no  share  in  reproduction,  but  perform  the 
manual  labor  for  the  colony,  searching  for  food, 
building  the  hive,  caring  for  the  young,  etc.  It  is 
this  last  class  that  concerns  us.  The  worker  bees  are 
very  different  from  the  other  classes.  Not  only 
have  they  different  instincts,  which  impel  them  to 


238  EVOLUTION  OF  TO-DAY. 

entirely  different  modes  of  life,  but  the  form  of 
their  body  is  entirely  different.  Indeed,  workers 
differ  more  from  the  males  and  females  of  the  same 
colony  than  do  different  species  from  each  other. 
Nor  is  this  all,  for  the  workers  may  not  only  differ 
from  the  males  and  females,  but  also  from  each 
other  to  such  an  extent  that  several  castes  of  work- 
ers are  sometimes  found.  In  some  cases  there  are 
three  castes  of  these  workers,  so  that  the  colony 
contains  five  sorts  of  individuals.  Nor  do  these 
castes,  as  a  rule,  graduate  into  each  other  ;  they  are 
perfectly  distinct,  as  much  so  indeed  as  any  two 
genera  of  the  same  family. 

Unquestionably  all  of  this  differentiation  is  of 
advantage  to  the  colony  ;  but  how  is  natural  selec- 
tion to  explain  the  origin  of  these  castes  of  workers  ? 
The  difficulty  lies  in  the  fact  that  the  workers  are 
sterile,  and  the  possibility  of  their  transmitting 
favorable  variations  to  another  generation  is  out  of 
the  question.  If  these  individuals  had  been  fertile, 
the  explanation  would  have  been  that  they  were 
acquired  slowly  by  natural  selection,  which  preserved 
the  favored  individual  and  thus  caused  their  peculi- 
arities to  be  transmitted  to  other  generations.  But 
the  insects  are  not  fertile,  never  have  any  descend- 
ants, and  consequently  cannot  transmit  their  peculi- 
arities, and  it  would  therefore  seem  that  they  could 
not  be  preserved.  How  then  could  these  castes 
have  arisen?  The  only  answer  is  to  consider  the 
whole  colony  as  an  individual,  and  the  various  castes 
as  organs.  In  other  animals  it  is  not  difficult  to  see 
how  any  organ  can  be  modified.  If  it  is  of  advan- 


STERILE  INSECTS.  239 

tage  to  the  individual,  that  a  certain  part  be  modi- 
fied  in  any  direction,  we  can  understand  how  this 
may  be  done  by  the  selection  of  individuals  with 
favorable  variations.  The  various  organs  do  not 
reproduce,  and  may  be  compared  to  the  working 
castes  of  insects.  It  is  possible  thus  to  look  upon 
the  whole  colony  as  an  individual,  the  males  and 
females  as  the  reproductive  organs,  and  the  workers 
corresponding  to  other  organs.  If  now  it  be  of  ad- 
vantage to  the  colony  that  these  working  organs 
should  be  differentiated  into  castes,  the  colonies 
which  presented  favorable  variations  in  this  direc- 
tion will  be  naturally  selected,  while  those  colonies 
which  do  not  have  such  variations  will  be  extermi- 
nated in  the  struggle  for  existence.  Or,  to  put  it  in 
other  terms,  the  females  which  have,  in  times  past, 
produced  young  showing  a  tendency  toward  differ- 
entiation into  castes  of  workers,  will  have  been  able 
to  form  colonies,  while  the  females  whose  offspring 
did  not  show  this  tendency  toward  differentiation 
will  not  have  been  able  to  form  colonies.  Those 
queen  bees  which  did  produce  differentiated  young, 
and  consequently  did  form  colonies,  would  eventu- 
ally give  birth  to  other  females,  and  these  females 
of  the  second  generation  will  in  turn  have  inherited 
the  same  tendency  from  their  parent.  On  the  other 
hand,  bees  which  could  not  form  colonies  would  not 
have  been  able  to  produce  other  generations,  and 
would  thus  have  become  extinct.  When,  then,  we 
look  upon  the  colony  as  an  individual,  and  the 
castes  as  organs,  the  difficulty  is  not  insoluble. 
This  explanation  is  certainly  very  ingenious,  and 


240  EVOLUTION  OF  TO-DAY. 

is,  moreover,  perfectly  logical  and  consistent.  The 
only  objection  to  receiving  it  is  the  same  that  we 
have  seen  in  other  cases.  The  results  are  too  great 
for  the  explanations.  It  is  hardly  possible  to  be- 
lieve that  natural  selection  acting  on  only  one  indi- 
vidual of  the  colony,  the  queen — and  not  upon  her 
directly,  but  only  through  her  attendants, — could 
have  had  so  great  an  effect.  Individual  variations 
could  have  here  no  influence.  Indeed,  Darwin,  who 
suggested  this  explanation,  probably  had  no  idea 
that  individual  differences,  or  differences  in  a  few 
workers,  could  ever  have  had  any  effect  on  the 
colony,  but  rather  that  those  queens  producing  off- 
spring, a  large  majority  of  which  showed  this  ten- 
dency toward  differentiation  into  castes,  would  be 
better  fitted  for  forming  colonies  than  those  whose 
offspring  showed  no  such  tendency,  or  showed  it 
only  in  a  few  cases.  Here,  therefore,  Darwin  would 
admit  the  necessity  of  assuming  that  the  variations 
were  considerable  in  amount,  and  occurred  in  many 
individuals  simultaneously.  Upon  any  other  suppo- 
sition this  explanation  is  palpably  insufficient,  for 
individual  variation  can  mean  nothing ;  only  those 
occurring  in  hundreds  of  animals  at  once  can  be  of 
any  moment. 

Summary. 

Natural  Selection,  or  the  Survival  of  the  Fittest, 
was  the  first  explanation  ever  offered  to  account  for 
the  origin  of  species  according  to  natural  laws.  It 
was  this  explanation,  so  simple  and  intelligible,  and 
yet  so  significant,  which  caused  evolution  to  obtain 


SUMMARY.  241 

such  firm  support  and  to  be  so  intimately  connected 
with  Darwinism.  But,  nevertheless,  natural  selec- 
tion has,  with  further  study,  proved  inadequate  to  the 
task  which  it  attempts  to  solve.  No  one  will  deny 
that  it  is  a  potent  factor  in  nature,  perhaps  the  most 
potent  which  has  been  yet  discovered ;  but  there  is 
much  disagreement  as  to  the  limits  of  its  power. 
While  Darwin  would  believe  it  the  all-important 
factor,  making  every  thing  else  subservient  to  it, 
other  scientists  would  consider  it  as  secondary  and 
of  little  importance.  We  have  seen  that  even  when 
we  admit  the  efficacy  of  the  law  in  nature,  it  lacks  a 
complete  explanation.  It  is  based  upon  the  exist- 
ence of  variations  which  are  themselves  unexplained. 
To  be  sure  these  variations  do  undoubtedly  occur, 
as  any  one  acquainted  with  animals  and  plants  is 
well  aware,  and  it  is  easy  to  conceive  that  the  in- 
finite variety  of  circumstances  under  which  different 
animals  are  placed  should  cause  varieties  in  bodily 
structure.  Such  variations  will  have  no  relation  to 
the  needs  of  the  animal,  will  be  indefinite  in  direc- 
tion, occurring  in  only  few  individuals  at  a  time*  and 
usually  of  slight  importance.  Unless  we  can  give 
a  more  fundamental  explanation,  such  indefinite 
variations  are  all  that  can  be  assumed.  With  these 
variations  Darwin  has  attempted  to  account  for  the 
origin  of  species,  but,  as  we  have  seen,  he  does  not 
completely  succeed.  If  species  have  always  arisen 
slowly  by  minute  variations,  as  they  seem  to  be 
doing  to-day,  the  time  since  the  solidifying  of  the 
world  has  not  been  long  enough  to  account  for  the 
present  species.  The  numerous  transitional  links 


242  EVOLUTION  OF  TO-DAY. 

between  species,  which  must  have  existed  according 
to  this  theory,  are  not  forthcoming  in  the  fossil 
records,  requiring  thus  a  great  burden  to  be  thrown 
upon  the  imperfection  of  this  history.  Many  spe- 
cies are  distinguished  by  features  of  no  use  to  them, 
and  these  never  could  have  been  developed  by 
natural  selection  alone.  It  is  mathematically  demon- 
strable that  single  variations  could  not  give  rise  to 
permanent  varieties,  but  would  tend  to  disappear  in 
successive  generations  'by  crossing,  and  not  to  in- 
crease as  would  seem  necessary  on  the  theory.  It 
is  therefore  absolutely  necessary  to  assume  that 
variations  occur  in  numerous  individuals  simultane- 
ously, and  to  find  a  reason  why  this  should  be  so, 
before  the  question  is  satisfactorily  answered.  The 
evidence  which  indicates  that  we  must  look  for 
some  internal  factor,  is  conclusive.  The  difficulty  of 
accounting  for  the  beginning  of  organs  without  some 
such  assumption,  the  difficulty  of  seeing  how  minute 
variations  could  be  of  enough  importance  to  be 
preserved  by  natural  selection,  the  independent 
development  of  similar  highly  developed  organs  in 
widely  separated  animals,  all  serve  to  strengthen  the 
belief  that  we  must  look  to  the  organism  itself,  in 
part,  for  the  laws  governing  the  origin  of  species. 
Finally,  when  we  consider  that  any  variation,  in 
order  to  be  preserved,  must  be  of  enough  import- 
ance to  regulate  the  life  or  death  of  the  species,  it 
becomes  almost  impossible  to  see  how  various  struc- 
tures of  morphological  species,  or  how  the  various 
castes  of  sterile  insects  could  ever  have  been  devel- 
oped upon  this  principle  alone. 


SUMMAR  Y.  243 

Natural  selection,  or  Darwinism,  is  therefore  al- 
most everywhere  acknowledged  as  insufficient  to 
meet  the  facts  of  nature,  since  many  features  of  life 
cannot  be  explained  by  it.  Even  Darwin  did  not 
consider  it  as  a  final  explanation,  placing  less  cre- 
dence upon  it  than  did  some  of  his  followers.  In 
his  later  works,  he  did  not  hesitate  to  acknowledge 
that  he  had  at  first  overrated  its  influence.  This 
admission,  and  the  conclusion  we  have  now  reached, 
does  not  detract  from  the  importance  of  the  prin- 
ciple, which  still  remains  as  one  of  the  important 
laws  regulating  organic  life.  The  question  now 
remains,  since  natural  selection  is  not  entirely  suffi- 
cient, can  any  other  explanation  be  offered  as  to 
the  laws  regulating  the  production  of  species  which 
will  supplement  Darwinism,  and  thus  bring  us 
nearer  the  true  solution  of  the  organic  world  ?  To 
this  question  we  now  proceed. 


CHAPTER  VII. 


MORE  RECENT  ATTEMPTS  TO  EXPLAIN  EVOLUTION. 

THE  objections  against  natural  selection,  sketched 
in  the  last  chapter,  are  very  formidable,  and  when 
taken  together,  amount  to  practical  proof  that  this 
principle,  as  originally  conceived,  is  inadequate  to 
explain  the  organic  world  as  we  now  see  it.  It  is 
impossible  to  believe  that  the  natural  selection  of 
indefinite  chance  variations  could  have  produced 
the  present  species  in  their  entirety.  But  indefinite 
chance  variations  are  all  that  Darwin's  theory  sup- 
plies as  its  basis  of  development.  Plainly,  then, 
Darwinism  must  be  supplemented  by  something 
else.  We  have  seen  in  the  first  five  chapters  that, 
since  the  appearance  of  the  "  Origin  of  Species,"  the 
evidence  for  evolution  has  been  growing  stronger 
and  stronger,  while  the  objections  have  been  disap- 
pearing. But  we  find  also  that  during  this  same 
period  the  difficulties  in  the  way  of  the  acceptance 
of  Darwin's  explanation  have  increased  rather  than 
diminished.  His  theory,  which  at  first  seemed  so 
readily  to  fill  the  need  which  was  felt,  has  been 
found  lacking  in  so  many  points  that  it  can  no 
longer  be  regarded  as  satisfactory.  It  must  be  re- 
membered, however,  that  it  was  the  followers  of 


ATTEMPTS    TO  EXPLAIN  EVOLUTION.       245 

Darwin  rather  than  Darwin  himself  who  believed  in 
the  universal  power  of  natural  selection.  Darwin 
did  not  even  at  first  claim  that  his  law  would  ex- 
plain every  thing,  and  in  his  later  works  he  admits, 
with  exemplary  candor,  that  he  had  formerly 
overrated  its  power  to  produce  changes.  He  still 
considered  it  to  be  the  most  important  factor  in  the 
development  of  species,  although  he  acknowledged 
that  the  difficulties  were  greater  than  he  had  at  first 
thought. 

While,  then,  the  theory  of  evolution  as  a  method 
of  creation  has  become  quite  firmly  established,  the 
explanation  offered  for  the  theory  has  almost  disap- 
peared. But  it  is  little  satisfaction  to  admit  the 
theory  if  it  is  no  longer  intelligible.  If  it  is  impos- 
sible to  tell  any  thing  about  the  laws  which  have 
governed  the  modifications  of  the  animal  kingdom, 
science  is  not  much  better  off  than  it  was  before. 
It  was  natural  selection,  and  not  evolution,  which 
made  Darwin  a  leader  in  modern  science.  Since 
this  principle  can  no  longer  be  regarded  as- satisfac- 
tory, naturalists  have  been  everywhere  searching  to 
discover  some  laws  which  may  supplement  it,  and 
enable  it  to  meet  the  difficulties  raised.  No  one 
would  be  inclined  to-day  to  deny  that  natural  selec- 
tion is  a  law  of  nature,  and  that  many  changes  are 
induced  by  it.  But  while  some  believe  it  to  be  the 
all-important  law  of  organic  life,  others  would  con- 
sider it  a  secondary  and  very  subordinate  principle, 
whose  effect  is  of  little  importance.  Between  these 
two  extremes  all  grades  may  be  found. 

It  is  much  easier  to  raise  objections  to  theories 


246  EVOLUTION  OF  TO-DAY. 

than  to  improve  them  or  make  new  and  better  ones. 
No  writer  has  had  any  difficulty  in  objecting  to  nat- 
ural selection,  but  very  few  have  been  able  to  sug- 
gest any  valuable  supplement,  or  still  less  to  advance 
any  new  theory  better  suited  to  the  facts.  Most 
scientists,  while  declining  to  accept  the  selection 
principle,  acknowledge  their  inability  to  offer  any 
other.  Not  a  few,  however,  have  offered  sugges- 
tions and  hypotheses  as  to  the  workings  of  nature 
in  producing  species,  suggestions  sometimes  of  value 
but  sometimes  worthless.  To-day  hardly  two  scien- 
tists would  exactly  agree  in  their  belief  in  the  method 
by  which  the  evolution  of  species  is  brought  about. 
It  is  our  purpose  now  to  consider  several  of  the 
most  important  additions  which  have  been  sug- 
gested as  aiding  natural  selection  in  producing  the 
present  species,  or  as  acting  by  themselves  inde- 
pendently of  Darwin's  law. 

It  may  perhaps  seem  like  a  hopeless  task  to  at- 
tempt to  answer  these  questions.  Science  has  little 
expectation  of  being  able  to  explain  life.  It  is  quite 
probable,  therefore,  that  after  having  investigated 
this  question  of  the  origin  of  species  to  the  utmost, 
it  will  be  eventually  necessary  to  fall  back  upon 
some  unexplored  land,  just  as  has  been  found  neces- 
sary in  all  other  departments  of  science.  But  this 
should  not  hinder  us  from  following  the  problem  as 
far  as  the  ability  of  human  reason  permits. 

It  is  first  necessary  to  notice  that  there  are  still  a 
few  scientists  who  accept  natural  selection  to  its 
fullest  extent.  They  refuse  to  admit  that  the  diffi- 
culties are  more  than  superficial,  and  they  carry  the 


THEORY  OF  MIGRATION.  247 

theory  even  further  than  did  Darwin.  The  only 
scientists  of  note  who  advocate  this  autocracy  of 
the  selection  theory  are  Haeckel  and  O.  Schmidt. 
But  Haeckel  is  always  too  full  of  startling  theories 
to  be  a  safe  guide,  and  Schmidt,  from  certain  state- 
ments recently  published,  would  not  be  disinclined 
to  admit  the  inadequacy  of  the  selection  principle 
in  some  cases.  Besides  these  scientists,  there  are 
the  extreme  materialists,  who,  reducing  every  thing 
to  matter,  are  obliged  to  find  in  natural  selection 
and  the  theory  to  be  mentioned  in  the  next  para- 
graph, the  efficient  causes  of  all  organic  phenomena. 
But  with  these  exceptions  pure  Darwinism  is  no 
longer  accepted. 

Theory  of  Migration. 

The  first  additional  bit  of  explanation  which  we 
notice  is  that  of  Moritz  Wagner.  We  have  seen 
that  one  of  the  greatest  difficulties  with  the  selec- 
tion theory  is  due  to  the  fact  that  crossing  always 
tends  to  eliminate  variations.  An  individual  with  a 
favorable  variation  will  almost  always  be  obliged  to 
cross  with  an  unfavored  individual,  and  this  will 
cause  the  variations  to  diminish  rather  than  increase. 
Wagner  attempts  to  avoid  this  difficulty  by  his 
theory  of  isolation  by  migration.  It  is  a  demon- 
strable fact  that  when  an  animal  or  plant  is  isolated 
from  other  members  of  the  same  species,  there  is  an 
increase  in  the  development  of  varieties.  Pigeons, 
in  the  hands  of  pigeon  fanciers,  are  in  a  condition 
of  practical  isolation,  since  the  varieties  are  pre- 
vented from  crossing  with  each  other.  A  glance  at 


248  EVOLUTION  OF  TO-DAY. 

the  numerous  breeds  of  pigeons  indicates  the  value 
of  such  isolation  in  producing  change.  Wagner, 
therefore,  believes  that  the  only  conditions  where 
new  species  can  arise  is  where  one  or  two  individ- 
uals are  by  some  sort  of  isolation  prevented  from 
crossing  with  others  of  the  same  species.  He  sug- 
gests that  if  we  suppose  a  small  number  of  indi- 
viduals, or  perhaps  a  single  pair,  to  migrate  into  a 
new  country,  and  be  prevented  from  returning,  such 
an  isolation  will  be  obtained.  All  injurious  crossing 
will  be  prevented.  The  offspring  of  this  pair  will 
be  obliged  to  breed  with  each  other,  and  thus  any 
variations  which  may  appear  will  have  the  chance 
to  accumulate.  For  a  time  all  of  the  offspring  will 
tend  to  have  the  same  variations,  since  produced 
under  the  same  conditions  by  the  same  parents. 
These  variations  will  not  then  be  eliminated  by 
crossing,  and  the  result  will  be,  therefore,  a  rapid 
development  of  a  new  species.  In  this  manner,  by 
eliminating  the  factor  of  crossing  favored  with  un- 
favored varieties,  one  of  the  most  fatal  objections 
to  Darwin's  theory  is  avoided.  Wagner  uses  his 
theory  to  account  for  the  origin  of  man  something 
as  follows  :  The  progenitors  of  man,  some  sort  of 
an  ape,  lived  in  tropical  Asia.  One  pair,  or  perhaps 
a  few  pairs,  migrated  from  their  home  in  the  north- 
ern part  of  the  continent,  and  their  return  was  pre- 
vented perhaps  by  glaciers.  This  pair  were  now  in 
a  very  different  climate,  and  were  obliged  to  strug- 
gle more  severely  for  their  existence  than  they  did 
in  the  luxurious  tropics.  This  active  struggle  pro- 
duced rapid  changes,  and  since  they  were  not  able 


THEORY  OF  MIGRATION,  249 

to  breed  with  the  original  unmodified  stock, 
the  variations  were  transmitted  and  augmented. 
This  finally  resulted  in  the  development  of  man, 
the  possibility  of  his  origin  arising,  according  to 
Wagner,  from  the  early  isolation  of  a  few  indi- 
viduals. 

Considering  the  series  of  facts  already  discussed, 
it  is  impossible  to  doubt  that  isolation  would  have 
something  of  the  effect  which  Wagner  supposes. 
Not  only  do  the  results  of  breeding  domestic  ani- 
mals show  this,  but  it  is  more  conclusively  shown 
by  the  fauna  of  oceanic  islands.  In  many  of  these 
islands,  as  we  have  seen  in  Chapter  V.,  there  is  almost 
a  complete  isolation  of  the  inhabitants  from  the  main 
land.  These  islands  have  been  originally  peopled 
by  migration,  and  the  individuals  have  been  sub- 
sequently isolated,  exactly  as  Wagner's  theory  as- 
sumes. We  have  already  seen  that  the  result  of 
this  isolation  is  the  production  of  new  species.  In 
all  cases  where  the  isolation  has  been  tolerably  com- 
plete there  has  been  a  remarkable  production  of  new 
species,  and,  if  the  time  has  been  long  enough,  of 
new  genera.  In  those  cases,  however,  where  the  iso- 
lation has  been  less  complete  and  there  has  been 
a  chance  of  continual  crossing  with  continental  spe- 
cies, new  forms  have  not  arisen.  Without  doubt 
isolation  has  had  its  influence  in  the  past,  and  we 
must  believe  that  Wagner's  theory  expresses  a  truth. 
But  to  ascribe  to  it  any  thing  more  than  a  subordi- 
nate position  is  not  possible.  There  are  some 
300,000  known  species  of  animals  living  to-day,  and 
to  suppose  that  they  all  could  have  arisen  by  such 


2$O  EVOLUTION  OF  TO-DAY. 

isolation  implies  an  amount  of  geographical  change 
which  is  absurd.  Moreover,  many  facts  tell  us  that 
such  isolation  is  not  necessary.  It  is  not  difficult  to 
find  examples  of  the  formation  of  two  or  more 
varieties  in  the  same  locality,  and  if  varieties  are 
incipient  species,  evidently  isolation  is  not  necessary 
for  their  formation.  In  the  Steinheim  lake  already 
referred  to,  we  have  an  instance  of  a  number  of  new 
species  being  formed  in  the  same  locality  without 
the  remotest  possibility  of  isolation.  Or  if  it  be 
claimed  that  the  Steinheim  species  are  simply  varie- 
ties, the  argument  is  still  the  same,  for  cross-breed- 
ing will  prevent  the  formation  of  varieties  just  as 
truly  as  it  will  prevent  the  formation  of  species. 
Wagner's  theory  of  isolation,  which  finally  led  its 
author  to  reject  natural  selection  entirely,  must  be 
admitted  as  a  factor  in  the  production  of  species. 
Isolation  will  in  many  cases  be  a  true  cause  of  the 
production  of  species  by  preventing  the  interbreed- 
ing of  modified  and  unmodified  varieties.  Still  no 
one  but  Wagner  would  claim  for  it  any  thing  more 
than  a  subordinate  position. 

Meehan  has  suggested  that  a  practical  isolation  of 
individuals  occurs  in  the  extreme  limits  of  the  distri- 
bution of  any  species.  Consider,  for  instance,  any 
plant  extending  in  great  numbers  over  a  large  terri- 
tory. In  the  centre  of  this  region,  so  numerous  will 
be  the  individuals  that  any  variation  will  be  im- 
mediately checked  by  cross-breeding.  But  upon  the 
boundary  of  the  territory  the  individuals  will  be 
so  few  in  numbers  that  the  offspring  of  the  same  in- 
dividual will  breed  with  each  other,  and  thus  would 


INTERNAL  FACTORS  IN  EVOLUTION.         251 

arise  a  practical  isolation  equal  in  its  efficacy  to  an 
actual  isolation. 

Internal  Factors  in  Evolution. 

Most  of  the  other  theories  of  evolution  which 
exist  at  the  present  day  attempt  to  answer  a  more 
fundamental  question  than  that  covered  by  natural 
selection.  Natural  selection  is  impotent  unless  it 
has  something  to  select,  and  all  later  theories  at- 
tempt to  explain  the  origin  of  variations.  American 
scientists  have,  more  than  any  others,  emphasized 
the  fact  that  the  survival  of  variations  is  a  matter 
secondary  to  their  origin,  and  it  is  becoming  realized 
more  and  more  that  this  is  the  point  to  be  explained. 
Darwin  hardly  attempted  to  answer  the  question  at 
all.  He  recognized  the  existence  of  variations,  and 
as  an  explanation  assumed  that  animals  and  plants 
have  a  tendency  to  vary.  It  must  not,  however,  be 
understood  that  he  was  satisfied  with  this  explana- 
tion. He  recognized  that  each  variation  had  its 
cause,  and  thought  that  these  causes  existed  in  the 
environment.  But  his  inability  to  discover  them 
taused  him  to  make  the  above  assumption  provision- 
ally, and  to  call  the  variations  due  to  chance.  We 
have,  however,  seen  that  it  is  no  longer  possible  to 
believe  in  an  evolution  founded  on  the  selection  of 
chance  variation.  It  becomes  necessary,  therefore, 
to  reduce  this  material  to  law,  and  the  theories  which 
we  are  now  to  consider  endeavor  to  do  this. 

It  is  plain  that  if  evidence  can  be  found  for  be- 
lieving that  variations  have  been  definite  in  direc- 
tion, and  have  effected  numerous  individuals  simul- 


252  EVOLUTION  OF  TO-DAY, 

taneously,  a  step  is  taken  toward  the  solution  of  the 
problem.  If  any  reason  can  be  found  why  variations 
should  thus  be  definite,  nearly  all  of  the  objections 
above  considered  will  disappear.  To  do  this,  scien- 
tists have  thought  it  necessary  to  find  some  internal 
forces  regulating  the  organism.  That  some  internal 
force  exists  seems  to  be  quite  conclusive.  It  is 
found  that  the  same  circumstances  do  not  always 
produce  the  same  variations.  Some  animals  vary 
much  under  circumstances  where  others  vary  very 
little.  Variations  of  any  species  are  not  abso- 
lutely indefinite,  but,  while  they  may  be  quite 
diverse,  are  still  found  in  definite  directions  ;  the 
horse,  for  example,  has  no  tendency  to  produce  horns. 
It  seems  hardly  questionable  that  there  have  been 
periods  of  rapid  modification  alternating  with  those 
of  comparative  rest.  We  have  seen  that  it  is  neces- 
sary to  assume  the  existence  of  some  sort  of  internal 
factor  to  explain  the  homology  of  serial  organs,  such 
as  that  of  the  arm  and  the  leg.  Something  of  the 
kind  is  needed  to  explain  the  independent  develop- 
ment of  the  same  complicated  organ  in  different 
animals,  such  as  the  vertebrate  and  mollusk  eye. 
Many  instances  are  known  of  a  large  number  of  ani- 
mals in  very  diverse  circumstances  varying  in  the 
same  direction.  All  Australian  marsupials,  for  ex- 
ample, have  shown  a  tendency  toward  the  reduction 
of  the  second  and  third  digits,  and  since  they  live 
under  very  different  circumstances  this  cannot  be 
due  wholly  to  the  environment.  All  such  facts  as 
these,  and  numerous  others  might  be  mentioned, 
which  certainly  indicate  that  there  is  something  be- 


THE  THEORY  OF  N A  CELL  253 

sides  the  external  conditions  regulating  the  varia- 
tions of  organisms. 

The  Theory  of  Nageli. 

In  regard  to  these  internal  laws  governing  the 
origin  of  variation,  science  is  profoundly  ignorant. 
Since  it  is  not  yet  possible  to  say  why  a  child  is  like 
its  parents,  it  is  certainly  difficult  to  understand 
why  it  should  be  different.  Most  theories  are  there- 
fore little  more  than  suggestions  thrown  out  as 
perhaps  indicating  a  truth,  but  as  requiring  more 
evidence  before  they  can  be  accepted. 

The  first  attempt  to  find  an  internal  force,  which 
we  notice,  is  that  of  the  German  botanist  Nageli, 
which  is  really  little  more  than  a  statement  that 
such  a  force  exists.  He  assumes  the  existence  in 
the  organism  of  an  internal  tendency  toward  pro- 
gression and  perfect  development,  and  believes  that 
in  accordance  with  this  tendency  organisms  are  con- 
stantly varying  in  such  a  manner  as  to  rise  in  the 
scale  of  nature.  Here  is  postulated  an  internal 
force,  which,  if  it  exist,  is  certainly  able  to  explain 
all  the  facts.  The  only  questions  are  whether  there 
is  any  evidence  for  the  existence  of  such  a  force,  and 
what  can  be  our  understanding  of  it  if  it  does  exist. 
Nageli  advances,  in  favor  of  his  view,  various  series 
of  facts  already  considered,  which  indicate  some  in- 
ternal force.  He  thinks  that  the  fact  of  a  continual 
progression  from  the  lower  to  the  higher  in  the  mod- 
ification of  species  is  evidence  that  some  definite 
tendency  to  advance  exists.  Natural  selection  only 
seems  to  make  animals  better  fitted  to  struggle  with 


254  EVOLUTION  OF  TO-DAY. 

their  enemies,  and  does  not  cause  them  to  rise.  He 
emphasizes  the  existence  of  the  development  of 
structures  which  are  of  no  use  to  their  possessor, 
and  believes  it  utterly  impossible  that  the  whole 
complicated  organism  of  higher  animals  and  plants 
could  have  been  built  up  from  unicellular  organ- 
isms without  an  innate  tendency  to  rise. 

But  no  one  of  these  points,  nor  all  of  them  to- 
gether prove  Nageli's  innate  tendency  toward  pro- 
gression. Most  of  them  we  have  already  sufficiently 
considered.  While  they  do  raise  difficulties  for 
Darwinism,  they  do  not  by  any  means  show  the  ex- 
istence of  any  law  similar  to  the  one  assumed.  The 
only  argument  which  needs  special  attention  is  the 
one  which  claims  that  the  fact  of  a  progression  in 
the  past  requires  such  a  tendency  to  rise.  To  this 
Darwin  has  answered  that  natural  selection  would 
also  imply  a  progression.  The  best  definition  which 
has  been  given  to  a  grade  of  organization,  is  the  de- 
gree to  which  the  parts  have  been  specialized  or 
differentiated.  Now  it  is  of  undoubted  advantage 
to  animals,  as  a  rule,  to  have  their  parts  specialized. 
Since  this  is  of  advantage,  natural  selection  will 
produce  an  advance  in  specialization.  It  is  not 
necessary,  therefore,  to  assume  any  innate  tendency 
to  rise  to  account  for  an  advance  in  organization. 
Moreover,  the  existence  of  such  a  constantly  acting 
tendency  is  disproved  by  the  fact  that  in  many  ani- 
mals there  has  been  a  degradation  in  structure. 
Many  individuals  living  to-day  are  lower  in  their 
organization  than  their  ancestors.  Parasitic  animals 
in  general  are  examples  of  this  class. 


THEORY   OF  EXTRAORDINARY  BIRTHS.       255 

The  chief  objection  to  Nageli's  theory  is,  how- 
ever, that  the  theory  is  more  difficult  to  understand 
than  the  facts  which  it  attempts  to  explain.  When 
we  attempt  to  imagine  to  ourselves  what  is  meant 
by  an  innate  tendency,  or  how  organisms  can  possess 
it,  we  see  at  once  that  the  theory  is  of  no  value 
toward  helping  to  an  understanding  of  the  problem. 
The  statement  that  organisms  have  an  innate  ten- 
dency toward  progression  is  simply  another  way  of 
saying  that  they  have  advanced,  and  are  still  advanc- 
ing, toward  greater  complication.  Nageli  recognized 
that  organisms  were  advancing,  saw  that  natural 
selection  was  not  sufficient  for  an  explanation,  and, 
to  comprehend  the  facts,  assumes  this  tendency,  of 
which  he  knows  nothing  and  can  know  nothing. 
At  best,  therefore,  it  gives  no  better  understanding 
of  evolution.  It  is  of  no  assistance  to  say  that  this 
tendency  was  placed  in  animals  by  the  Creator, 
until  we  can  get  some  idea  of  what  the  tendency  is 
and  how  it  can  be  transmitted  from  generation  to 
generation.  While  we  may  admit  that  such  a  ten- 
dency, if  it  existed,  would  explain  many  difficult 
problems,  we  must  realize  that  there  is  no  good 
evidence  for  its  existence,  and  that  its  very  mean- 
ing is  obscure.  To  attempt  to  explain  species  on 
such  a  theory  is  to  abandon  the  attempt  altogether, 
and  to  admit  the  problem  to  be  insoluble. 

Theory  of  Extraordinary  Births. 

Somewhat  akin  to  this  idea  of  Nageli's,  is  the 
theory  of  St.  George  Mivart.  Similar,  because  in 
like  manner  it  appeals  to  internal  causes  acting  on 


2$6  EVOLUTION  OF  TO-DAY. 

organisms,  of  whose  workings  we  know  nothing. 
Mivart,  after  marshalling  in  battle  array  all  of  the 
possible  objections  against  natural  selection,  comes 
to  the  conclusion  that  it  is  a  law  of  nature  of  lit- 
tle importance,  and  playing  only  a  secondary  and 
very  subordinate  part.  He  advances  in  its  place  a 
theory,  of  which  he  is  not,  indeed,  the  originator, 
though  he  is  its  chief  exponent.  Owen,  Kolliker, 
the  Duke  of  Argyle,  and  other  well-known  scientists, 
share  his  views.  He  thinks  species  have  arisen  sud- 
denly, by  extraordinary  births  and  not  by  slow  modi- 
fication. He  grants  that  a  very  great  amount  of 
variation  may  occur  in  any  species:  experiments 
with  domestic  animals  prove  this  too  conclusively  for 
denial.  But  he  thinks  that  these  variations  are  not 
indefinite  and  not  unlimited.  They  are,  in  his  view, 
always  in  certain  directions,  and  always  confined 
within  certain  bounds.  By  variation  alone,  he  says, 
no  new  species  ever  arise.  By  ordinary  variation 
many  cases  may  be  developed,  differing  from  each 
other  in  very  marked  degrees,  but  they  form  simple 
varieties,  are  always  within  the  bounds  of  the  species, 
and  never  become  so  different  as  to  be  sterile  when 
crossed.  Mivart  does  not  believe,  therefore,  that 
varieties  are  incipient  species.  Species  arise  by 
sudden  extraordinary  births.  An  animal  is  born 
which  differs  from  its  parents,  in  certain  respects,  so 
much  that  it  is  from  the  first  a  new  species.  It  is  a 
"  new  chord  in  nature."  As  to  the  laws  regulating 
such  births,  Mr.  Mivart  acknowledges  complete  igno- 
rance, but  he  thinks  that  enough  strange  births  are 
known  to  indicate  them  to  be  the  factor  sought. 


THEORY  OF  EXTRAORDINARY  BIRTHS.       2 57 

Examples  of  such  births  are  sufficiently  common 
arising  from  causes  not  at  all  understood.  Some  of 
them  are  to  be  considered  as  malformations ;  but  it 
is  not  impossible  that  even  such  features  should  oc- 
casionally be  of  enough  importance  to  be  the  origin 
of  a  new  species.  But  many  such  births  cannot  be 
considered  as  malformations.  Two  or  three  of  the 
best  instances  it  may  be  well  to  give  here. 

The  Ancon  sheep  is  a  breed  with  dwarfed  legs, 
and  it  made  its  appearance  thus  suddenly  :  A  Massa- 
chusetts farmer  found  a  single  ram  in  his  flock  in 
1791  which  possessed  dwarfed  legs.  Thinking  that 
such  a  peculiarity  might  be  valuable  in  preventing 
the  sheep  from  jumping  fences,  he  preserved  this 
ram  to  breed  from.  The  result  was  that  the  Ancon 
sheep  thus  arising  soon  supplanted  the  original 
variety.  It  was  found  that  when  the  Ancon  ram 
was  crossed  with  a  ewe  of  any  other  variety,  the  off- 
spring was  not  an  intermediate  variety  but  of  the  pure 
Ancon  type,  a  fact  which  will  be  seen  at  once  to  be 
of  extreme  importance,  since  it  shows  that  crossing 
will  not  always  eliminate  variations.  Dr.  Godron, 
of  Nancy,  upon  sowing  some  Datura  tatula,  whose 
fruit  is  covered  with  spines,  discovered  among  the 
plants  raised  an  individual  whose  seed  capsule  was 
smooth.  The  seeds  of  this  plant  were-  preserved 
and  again  sown,  and  all  of  the  plants  coming  from 
them  showed  the  same  peculiarity.  The  seeds  of 
the  next  generation  were  again  sowed  with  like  re- 
sult ;  and  so  on,  so  long  as  the  experiment  con- 
tinued. It  was  also  found  that  when  the  smooth 
variety  was  crossed  with  the  original  form  hybrids 


2$8  EVOLUTION  OF  TO-DAY. 

were  produced  resembling  true  hybrids  ;  and  in  the 
second  generation  they  reverted  to  the  original  type, 
just  as  is  the  case  in  true  hybrids  between  species. 
A  more  remarkable  case  still,  is  the  appearance  in 
five  distinct  cases  in  England,  of  a  special  new  breed 
of  peacock  known  as  the  black-shouldered  variety, 
which  was  so  different  from  the  ordinary  form  that 
Dr.  Sclater  regarded  it  as  a  distinct  species  This 
animal  was  produced  in  flocks  of  peacocks  composed 
entirely  of  the  ordinary  kind,  making  its  appearance 
suddenly  by  ordinary  generation.  This  variety  was 
allowed  to  remain  with  the  others  and  breed  freely 
with  them,  but  even  under  these  conditions,  in  some 
cases,  it  increased  in  numbers  until  it  replaced  the 
previously  existing  form.  These  three  instances 
will  serve  as  illustrations  of  extraordinary  births. 
Many  others  might  be  given,  most  of  which  have 
been  collected  by  Darwin,  who  is  the  greatest 
authority  on  variations  of  all  kinds.  Naturally  all 
of  these  instances  occur  in  domestic  animals  or  in 
plants,  for  it  would  be  impossible  to  distinguish 
them  among  wild  animals.  If  such  an  individual 
were  found  in  nature  there  would  be  no  means  of 
knowing  how  it  arose.  It  would,  of  course,  be  set 
down  as  a  new  variety  or  species  and  that  would  be 
all  that  would  be  known  about  it.  Probably  many 
such  individuals  have  been  found  and  are  in  our 
collections  now  ;  but  since  there  is  no  means  of 
telling  how  they  arose  they  are  called  examples  of 
rare  species. 

These    extraordinary  births   do   then  occur,  and 
Mr.  Mivart  thinks  they  represent  the  beginning  of  a 


THEORY  OF  EXTRAORDINARY  BIRTHS.       259 

new  species.  He  believes  further  that  all  species 
arise  somewhat  in  this  way.  He  recognizes  as  the 
foundation  of  these  births  an  internal  law  presiding 
over  the  action  of  every  part  of  every  individual 
and  of  every  organism  as  a  unit,  and  of  the  entire 
organic  world  as  a  whole.  "  By  such  a  force  from 
time  to  time  new  species  are  manifested  by  ordinary 
generation."  A  sudden  extraordinary  birth  takes 
place,  and  the  animal  thus  born  becomes  the  pro- 
genitor of  a  new  species. 

Such  a  theory  would  avoid  most  of  the  difficulties 
enumerated  in  the  preceding  chapters.  The  diffi- 
culty of  geological  time  is  evidently  no  longer  of 
any  importance,  since  species  appear  suddenly.  The 
absence  of  transitional  forms  between  existing 
species,  an  absence  which  we  have  seen  both  among 
fossils  and  living  forms,  is  no  longer  so  much  of  a 
surprise,  for  the  infinite  number  of  transitional 
forms  assumed  by  the  selection  theory  have  not 
existed  if  Mivart's  view  be  true.  The  difficulty  of 
conceiving  the  rudimentary  beginning  of  organs  and 
of  understanding  how  organs  could  be  built  up  by 
minute  stages  is  completely  avoided.  If  it  be  con- 
ceded, as  Mivart  believes  that  there  is  an  internal 
bond  uniting  animals  and  regulating  their  develop- 
ment, there  is  an  immediate  explanation  of  serial 
homology,  and  of  the  independent  origin  of  similar 
structures.  Highly  complicated  organs  no  longer 
become  a  trouble,  since  in  these  extraordinary  births 
considerable  changes  occur  at  once.  Finally,  the 
difficulty  of  the  elimination  of  variations  by  crossing 
is  largely  done  away  with,  since  observations  have 


260  EVOLUTION  OF  TO-DAY. 

shown  that  these  extraordinary  variations  may  be 
propagated  truly  even  when  the  individual  crosses 
with  unmodified  forms.  Indeed,  the  theory  of  sud- 
den births  succeeds  in  meeting  nearly  all  of  the 
difficulties  which  we  have  enumerated  in  the  pre- 
ceding chapters,  while  at  the  same  time  it  fills 
equally  well  the  necessities  of  the  evolutionary 
argument. 

This  theory  of  Mivart  is  a  sort  of  compromise 
between  evolution  and  special  creation.  It  grants 
the  genetic  connection  of  species,  and  is  thus  evolu- 
tion; but  it  assumes  this  sudden  and  separate  origin 
according  to  unknown  laws,  and  is  therefore,  in  a 
sense,  a  special-creation  theory.  Mr.  Mivart's  views 
are  brought  forward  with  a  clearness  and  force 
seldom  found  in  scientific  writings,  and  can  scarcely 
fail  to  carry  a  certain  amount  of  conviction.  But  it 
cannot  be  considered  that  this  theory  is  much  more 
satisfactory  than  the  others.  Unless  his  jumps  are 
enormous,  such,  for  instance,  as  the  sudden  develop- 
ment of  the  wing  of  the  bat  or  the  bird,  no  light  is 
thrown  on  the  origin  of  complicated  organs  or  the 
absence  of  transitional  links.  Such  jumps  as  these 
even  Mr.  Mivart  would  hardly  assume.  Moreover, 
the  facts  of  classification,  the  relationship  of  species, 
the  many  cases  of  fine  gradations  existing  between 
species,  the  impossibility  of  distinguishing  species 
and  varieties,  the  arrangement  of  species  into 
groups  and  sub-groups,  are  facts  which  indicate  that 
in  some  instances  at  least  species  have  arisen  by 
small  steps.  The  idea  of  sudden  jumps  is  not  in 
accordance  with  such  facts.  Mr.  Mivart  claims  too 


THEORY  OF  EXTRAORDINARY  BIRTHS.       261 

much  for  his  sudden  births.  That  this  factor  may 
have  had  its  influence  will  hardly  be  denied  by  any 
one,  and  in  some  cases  new  species  may  have  arisen 
in  accordance  with,  these  extraordinary  births.  This 
theory  has  so  many  facts  in  its  favor  that  it  seems 
as  if  it  must  have  a  certain  amount  of  truth.  But 
at  the  same  time  it  will  not  account  for  all  of  the 
facts  of  nature  and  some  of  the  difficulties  which  we 
have  seen  are  just  as  forcible  even  when  we  substi- 
tute these  sudden  jumps  for  the  minute  variations 
of  Darwinism.  While  every  one  acknowledges  that 
natural  selection  is  a  potent  factor  in  the  modifica- 
tion of  species,  scientists  refuse  to  consider  it  as 
more  than  one  factor.  And  in  the  same  way,  while 
it  seems  probable  that  sudden  extraordinary  births 
may  have  had  their  influence  in  the  origin  of  species, 
here  too  it  must  be  recognized  that  we  have  only 
a  single  factor. 

Indeed,  after  all,  this  theory  of  Mivart  does  not 
very  much  help  toward  a  solution  of  the  problem  of 
the  origin  of  species,  for,  like  the  theory  of  Nageli, 
it  does  not  explain,  but  refers  every  thing  to  un- 
known internal  forces.  To  be  sure,  in  this  case,  it  is 
a  demonstrated  fact  that  some  internal  force  exists, 
for  it  cannot  be  questioned  that  these  extraordinary 
births  do  sometimes  occur.  Since  we  believe  nature 
to  be  universally  governed  by  law,  even  these  ir- 
regular occurrences  must  be  under  the  influence  of 
some  law.  But  of  its  working  and  significance 
Mivart  can  tell  us  nothing.  We  have  seen  that 
natural  selection  is  lacking,  since  it  is  founded  on 
variations  which  it  cannot  explain.  The  same  ob- 


262  EVOLUTION  OF  TO-DAY. 

jection  is  even  more  forcibly  urged  against  Mivart's 
theory  since  these  extraordinary  births  are  more 
difficult  to  understand  than  are  simple  variations. 
The  appeal  to  an  internal  law  regulating  them  is  no 
explanation,  but  simply  a  method  of  avoiding  the 
question. 

Neo-Lamarckianism  :   Use  and  Effort. 

A  theory  more  intelligible  than  the  preceding, 
and  more  logical,  since  it  appeals  to  known  rather 
than  unknown  factors,  is  the  old  idea  of  Lamarck. 
This  theory  finds  in  use  and  effort  the  active  forces 
causing  the  modification  of  animals.  It  is,  perhaps, 
the  simplest  explanation  which  has  been  offered. 
Not  only  this,  but  it  was  the  first  suggestion.  La- 
marck, who  first  formulates  a  definite  evolution 
theory  used  this  idea  as  its  foundation.  But  the 
theory  did  not  find  favor  with  Darwin,  and  it  has, 
consequently,  received  little  support  until  within  a 
few  years.  It  has  of  late,  however,  been  taken  up 
by  various  American  scientists,  who,  having  made 
some  slight  modifications,  have  ably  supported  it. 
The  theory  as  held  to  day  has  been  called  neo- 
Lamarckianism,  and  may  be  regarded  as  the  Ameri- 
can school  of  evolution,  since  its  chief  supporters 
belong  to  this  continent.  Its  most  prominent  ad- 
vocates are  Cope  and  Hyatt. 

Neo-Lamarckianism  finds  the  primal  modifying 
factor  in  the  activities  of  animals  in  their  endeavors 
to  meet  the  requirements  of  changing  conditions. 
Something  is  attributed  to  the  direct  action  of 
chemical  and  physical  forces  produced  by  changes 


NEO-LAMARCKIANISM.  263 

in  food  or  physical  conditions.  But  the  chief  agencies 
in  producing  variations  are  habits  of  use  and  disuse 
of  various  parts.  Darwin,  indeed,  recognized  this 
factor,  but  believed  it  of  slight  importance.  Neo- 
Lamarckianism  regards  it  as  by  far  the  most  impor- 
tant factor. 

That  the  use  of  an  organ  has  great  influence  upon 
its  development  in  the  individual  so  using  it,  is  a 
fact  too  well  attested  to  admit  question.  The  size 
of  the  blacksmith's  arm,  the  general  development  of 
the  body  of  the  gymnast,  the  delicacy  of  the  blind- 
man's  feeling,  the  acuteness  of  the  musician's  ear, 
the  degeneration  of  any  organ  whose  use  has  dis- 
appeared— as  a  paralyzed  arm, — are  all  conclusive 
proofs  of  this  fact.  Now,  if  continual  use  of  an 
organ  results  in  an  increase  of  its  efficiency,  and  if, 
further,  the  offspring  of  the  animal  so  using  it  in- 
herits this  increased  efficiency,  it  is  evident  that  it 
is  no  longer  so  difficult  to  understand  the  develop- 
ment of  organs.  Physiology  teaches  us  why  it  is 
that  increased  use  has  this  effect.  Any  use  of  a 
part  above  the  normal,  causes  an  extra  amount  of 
blood  to  flow  to  that  part,  and  an  increased  activity 
of  its  various  cells.  If,  therefore,  any  organ  become 
of  new  value  to  its  possessor,  by  reason  of  any 
change  in  conditions,  it  will  be  used  more,  and 
so  long  as  it  is  thus  used,  its  activities  will  increase, 
and,  consequently,  its  size  and  efficiency.  If,  now, 
the  offspring  of  such  an  individual  has  a  tendency 
to  inherit  the  peculiarities  of  its  parents,  the  second 
generation  will  have  the  organ  in  question  better 
developed  to  start  with  than  did  its  parents.  During 


264  EVOLUTION  OF  TO-DAY. 

the  life  of  this  generation,  if  the  same  conditions 
remain,  use  will  still  further  increase  the  perfection 
of  the  organ,  and  the  third  generation  will  be  better 
endowed  than  the  second.  And  so  on,  by  continual 
use  any  part  will  increase  in  size,  and  there  will  thus 
constantly  arise  variations  or,  better,  regular  modifi- 
cations in  just  those  organs  where  development  is 
needed. 

This  theory  finds  the  modifying  cause  in  the 
activities  of  the  organism.  Any  form  of  motion, 
conscious  or  unconscious,  will  produce  its  effects. 
But  most  of  the  motions  of  animals  are  regulated 
by  consciousness  and  effort  on  the  part  of  the  ani- 
mal. This  school,  therefore,  finds  in  the  efforts  of 
the  individual  one  of  the  most  important  factors  in 
producing  variation.  The  statement  that  effort  is 
an  important  factor  in  evolution  is  liable  to  a  mis- 
understanding. It  is  frequently  thought  that  the 
theory  implies  that  animals  develop  certain  organs 
because  they  make  an  effort  to  do  so  ;  but  this  is 
so  much  beyond  the  power  of  animals  as  we  know 
them,  that  it  is  absurd.  But  the  theory  of  effort 
and  use  is  very  different.  Organs  develop  as  the 
result  of  effort,  it  is  true,  but  the  effort  is  directed 
toward  the  satisfying  of  certain  wants,  and  has  only 
an  indirect  relation  to  the  development  of  the  organ 
in  question.  An  animal  has  the  consciousness  of 
hunger,  and,  in  order  to  remove  this  painful  feeling, 
strives  to  reach  the  food  on  the  branches  above  its 
head.  As  a  result  from  the  continuation  of  this 
effort  and  consequent  strain,  the  neck  is  lengthened. 
Or  an  individual  endeavors  to  escape  from  its  ene- 


NEO-LAMARCKIANISM.  26$ 

mies  by  running  from  them.  This  is  the  effort 
on  the  part  of  the  animal ;  but  the  result  is  the 
strengthening  and  increase  in  size  of  the  muscles  of 
the  legs,  and  the  individuals  become  better  adapted 
for  running.  And  so  in  general.  The  effort  is  to 
satisfy  certain  wants,  and  the  result  is  the  develop- 
ment of  new  activities.  Hence  the  modification  of 
organs  by  use. 

To  make  this  theory  of  use  and  effort  of  any 
significance  (the  same  may  be  said  in  regard  to 
Darwin's  theory),  it  is  necessary  to  assume  that 
the  child  has  a  tendency  to  inherit  these  pecu- 
liarities at  an  earlier  age  than  they  were  acquired 
by  the  parent.  This  law,  which  is  called  the  law 
of  accelerated  development,  causes  the  variations 
arising  by  use  or  otherwise  to  be  inherited  at 
earlier  and  earlier  ages  as  generations  go  by.  An 
increase  in  the  size  of  an  organ  first  acquired  in 
middle  life  would,  after  a  number  of  generations,  be 
possessed  by  the  young.  For  example :  the  large 
arm  of  the  blacksmith  is  acquired  during  manhood, 
but,  according  to  the  law  in  question,  the  children 
would  have  a  tendency  to  develop  this  large  arm  at 
a  slightly  earlier  period.  If  they  followed  the  same 
trade,  their  children  would  inherit  the  same  peculi- 
arities still  earlier.  And  if  the  family  continued  to 
follow  the  trade  of  blacksmith,  the  peculiarity  would 
be  carried  back  to  the  young,  and  the  children 
would  show  from  their  birth  that  they  were  black- 
smiths. This  principle  of  acceleration  is  believed 
by  some  to  be  universal.  By  others  it  is  regarded 
as  not  universal,  since  in  certain  cases  they  think  an 


266  EVOLUTION  OF  TO-DAY. 

actual  retardation  has  taken  place.  It  is  evident 
enough  that  acceleration  must  be  the  general  rule. 
The  fact  that  embryology  repeats  past  history,  is  a 
sufficient  proof  of  this,  for  such  a  repetition  would 
be  impossible  without  such  a  law. 

Neo-Lamarckianism  would,  therefore,  tell  us  that 
one  of  the  most  important  factors  in  the  modifica- 
tion of  organisms  is  consciousness,  which  is  the  cause 
of  various  activities.  Cope  regards  consciousness  as 
one  of  the  fundamental  properties  of  protoplasm. 
He  thinks  that  all  activities,  even  those  now  auto- 
matic, such  as  the  circulation  of  the  blood,  were 
originally  acquired  by  conscious  effort.  But  at  all 
events  it  is  plain  that  consciousness  does  regulate 
the  use  or  disuse  of  organs,  and  hence  if  this  theory 
is  true,  it  is  a  very  potent  factor.  Food  becomes 
scarce  in  any  locality,  and  animals,  driven  by  their 
hunger,  migrate  into  new  regions,  where  they  find 
new  conditions  and  new  enemies  to  contend  with. 
In  their  endeavors  to  meet  the  new  conditions  they 
acquire  new  activities,  and  these  cause,  by  the  prin- 
ciple of  use,  variations  to  appear.  All  individuals 
thus  circumstanced  will  be  affected  in  the  same  way, 
and  there  thus  arise  simultaneous  variations,  which 
may  be  preserved  or  rejected  by  natural  selection. 

It  is  plain  that  this  theory  is  more  applicable  to 
animals  than  to  plants.  The  motions  of  plants  are 
slight,  and  their  consciousness  is  very  questionable. 
Use  and  effort  would  have  little  effect  here.  Still 
to  a  certain  extent  it  is  believed  to  apply  even  here. 
Plants  do  have  a  certain  amount  of  motion  of  their 
various  parts,  leaves,  tendrils,  etc.  The  sap  is  con- 


NEO-LAMARCKIANISM.  267 

stantly  in  motion.  Low  plants  move  freely  from 
place  to  place.  The  visitation  of  insects  produces 
indirectly  a  certain  amount  of  motion  which  has  its 
influence.  Even  in  plants,  therefore,  the  activities  of 
the  individual  may  be  the  important  origin  of  varia- 
tion. 

This  whole  theory  is  very  simple  and  logical.  But 
there  is  one  point  which  must  be  more  definitely 
proved  before  use  can  be  accepted  as  having  the  far- 
reaching  influence  here  supposed.  It  must  be  more 
surely  demonstrated  that  animals  do  inherit  the 
effects  of  use  and  disuse.  That  use  does  increase 
the  size  of  organs  in  the  individual  using  them  can 
not  be  questioned ;  but  it  is  by  no  means  so  certain 
that  this  effect  is  transmitted  to  the  next  generation. 
The  blacksmith  develops  a  large  arm,  but  the  arms 
of  his  children  are  no  larger  than  those  of  other 
children.  It  is  indeed  very  seldom  that  any  direct 
evidence  can  be  obtained  of  the  inheritance  of 
acquired  variations  of  this  character.  Darwin,  with 
the  vast  amount  of  evidence  at  his  command,  was 
inclined  to  think  that  they  were  not,  as  a  rule,  trans- 
mitted, and  that,  therefore,  this  principle  was  of 
little  importance.  He  has  given  some  instances, 
however,  which  he  ascribes  to  the  effect  of  use  or 
disuse.  Rudimentary  organs,  for  instance,  can  be 
explained  in  no  other  way.  But  the  direct  evidence 
of  observation  would  hardly  be  expected,  even  if 
the  theory  were  true,  since  the  effects  of  inherited 
use  would  be  so  difficult  to  distinguish  from  those 
of  actual  use.  In  order  that  a  blacksmith's  children 
should  show  any  marked  difference,  it  would  be 


268  EVOLUTION  OF  TO-DAY. 

necessary  that  the  trade  of  blacksmith  should  be 
followed  by  the  same  family  for  many  generations, 
and  who  could  tell  at  first  how  much  the  young 
smith  owed  the  large  size  of  his  arm  to  inheritence, 
and  how  much  to  direct  use  ?  But  our  American 
scientists  have  collected  many  instances  which  show 
that  the  effects  of  use  are  inherited.  One  example 
is  the  shape  of  the  teeth  of  ungulates.  A  careful 
study  has  shown  that  the  shape  of  the  tubercles  of 
their  teeth  is  exactly  such  as  would  have  resulted 
from  the  motions  of  their  jaws.  Different  groups 
of  ungulates  have  different  shaped  teeth  ;  but  the 
motion  of  their  jaws  is  also  different,  and  the  two 
are  found  to  be  correlated.  Now  since  these  tubercles 
appear  while  the  animal  is  very  young,  they  must 
be  due  to  inheritance.  And  since  it  is  hardly  pos- 
sible to  conceive  them  of  enough  importance  to  be 
developed  by  natural  selection,  it  is  claimed  that 
they  are  instances  of  the  inherited  effect  of  use.  A 
number  of  cases  of  similar  import  have  been  ad- 
vanced as  proofs  of  the  fact,  so  necessary  for  the 
neo-Lamarckiann  theory,  that  the  effects  of  use  and 
disuse  are  inherited. 

This  brings  us  to  a  final  question,  which  really 
lies  at  the  bottom  of  the  whole  matter.  What  are 
the  laws  of  heredity  ?  What  sort  of  characters  does 
an  animal  inherit  from  its  parents?  We  can  cer- 
tainly find  abundant  variations  arising  either  from 
the  indefinite  variability  of  Darwin,  the  extraordi- 
nary births  of  Mivart,  or  the  effects  of  use  and 
effort.  Are  these  variations  all  inherited  ?  The 
final  question  is  thus  the  explanation  of  heredity. 


HEREDITY. — THEORY  OF   WEISMANN.       269 

If  we  can  find  out  the  reason  why  a  child  is  like 
its  parents,  we  shall  doubtless  know  why  he  is  dif- 
ferent in  certain  respects.  Scientists  are  searching 
to-day  after  some  explanation  of  heredity.  Already 
several  hypotheses  have  been  advanced ;  but  it  will 
be  admitted  that  they  are  only  hypotheses,  more  or 
less  probable,  but  usually  created  to  fit  the  facts, 
instead  of  being  called  for  by  them.  None  of  them 
are  far  enough  advanced  to  be  rightly  called  theo- 
ries, and  it  would  as  yet  be  impossible  to  find  any 
two  scientists  who  agree  upon  any  positive  conclu- 
sion on  this  matter.  Of  the  various  hypotheses, 
probably  not  one  is  fully  accepted  by  any  person  but 
its  author.  These  theories  are,  however,  a  neces- 
sary part  of  the  explanation  offered  for  evolution, 
and  it  is  desirable  before  closing  this  account  of  the 
theories  of  evolution  to  consider  at  least  two  of 
them  which  bear  particularly  upon  the  subject 
we  are  considering. 

Heredity. —  Theory  of  Weismann. 

In  looking  at  this  question  of  heredity,  we  find, 
to  start  with,  that  not  only  are  the  explanations  of 
the  law  in  dispute,  but  even  the  facts  are  by  no 
means  agreed  upon.  That  an  animal  can  inherit 
from  its  parents,  is  everywhere  admitted  j.  but  be- 
yond this  very  general  statement  there  is  little 
unanimity  of  opinion.  Whether  it  can  inherit  all 
sorts  of  peculiarities,  or  only  certain  definite  kinds ; 
whether  it  inherits  from  both  parents  alike,  or  from 
only  one ;  or  whether  one  sort  of  traits  is  inherited 
from  the  male  parent,  and  another  from  the  female 


270  E.VOLUTION  OF  TO-DAY. 

parent,  are  points  yet  in  dispute.  More  important 
still  is  the  question  whether  an  animal  is  able  to  in- 
herit from  its  parents  any  features  newly  acquired  by 
them,  i.  e.,  any  peculiarity  which  its  parents  ac- 
quired after  reaching  their  adult  condition,  such  as 
accidental  mutilations,  etc.  These  variations  are 
known  as  acquired  variations,  and  it  is  still  a  ques- 
tion not  definitely  settled  how  far  they  can  be  trans- 
mitted from  one  generation  to  another.  It  might 
seem  that  these  points  wonld  be  easy  enough  to 
settle  by  simple  observation,  and  doubtless  every 
one  will  call  to  mind  instances  which  seem  to  prove 
the  truth  of  some  of  these  positions.  But  so  many 
modifying  circumstances  arise  to  vitiate  the  results, 
and  so  contradictory  are  the  various  facts  observed, 
that  it  has  been  found  thus  far  impossible  to  come 
to  any  unanimous  conclusion  even  on  these  simple 
questions  of  fact. 

The  first  hypothesis  which  we  notice  is  that  of 
the  German  naturalist  Weismann.  This  we  con- 
sider first,  not  because  it  is  the  oldest,  for  it  is  the 
most  recent  theory ;  but  because  it  is  the  simplest, 
and  has  a  direct  bearing  upon  the  theories  of  evolu- 
tion. In  his  explanation  Weismann  turns  for  assist- 
ance to  the  lowest  animals  and  plants — the  unicel- 
lular organisms,  in  which  reproduction  is  the  simple 
result  of  growth.  In  these  animals — the  amoeba, 
for  instance — the  body  consists  of  a  small  bit  of 
protoplasm,  without  much  differentiation  into  parts. 
Having  no  mouth  nor  respiratory  organs,  they  must 
absorb  all  of  their  food  and  gases  through  the  sur- 
face of  the  body.  Now,  by  a  well-known  mathe- 


HEREDITY. — THEORY  OF  WEISMANN.        2/1 

matical  principle,  when  the  body  increases  in  size, 
the  surface  increases  as  the  square  of  the  dimensions, 
while  the  bulk  increases  as  their  cube.  The  bulk  of 
the  animal  increases,  therefore,  faster  than  the  ab- 
sorptive surface.  The  animal  continues  feeding  and 
growing,  until  it  finally  reaches  a  size  when  its  bulk 
is  too  great  to  be  kept  supplied  with  the  nourish- 
ment absorbed  by  its  surface.  When  this  limit  is 
reached,  the  body  simply  breaks  into  two  pieces, 
each  of  which  becomes  independent,  and  goes  on 
feeding  precisely  as  did  the  original  animal,  until 
once  more  the  limit  is  reached.  Here  is  a  simple 
form  of  heredity,  and  there  is  no  difficulty  in  under- 
standing it.  Each  of  the  resulting  individuals  is  like 
the  other,  and  like  the  original,  because  each  is  half 
of  this  original.  And  there  is,  therefore,  no  reason 
why  they  should  be  unlike.  Now,  with  this  simple 
case  in  our  minds,  it  is  not  difficult  to  explain 
heredity  in  higher  animals.  Every  animal,  let  us 
for  convenience  say  man,  is  derived  from  an  ovum, 
which  is,  like  the  amoeba,  a  single  cell  composed  of 
a  mass  of  protoplasm.  Of  course,  this  ovum  differs 
from  the  amoeba  in  possessing  the  power  to  develop 
into  a  complicated  man,  but,  nevertheless,  it  is  a 
single  cell,  and  in  this  sense  the  two  are  strictly 
comparable.  When  this  ovum  begins  to  develop 
toward  the  adult,  the  first  change  that  takes  place  is 
its  division  into  two  parts.  Now,  remembering  the 
former  case,  Weismann  says  that,  just  as  it  was  not 
difficult  to  see  how  the  two  halves  of  the  divided 
amoeba  were  alike,  so  it  is  not  difficult  to  understand 
here  how  each  half  of  the  divided  ovum  is  like  the 


272  EVOLUTION  OF  TO-DAY. 

other  half,  and  hence  like  the  original  ovum.  The 
original  ovum  was  capable  of  developing  into  a  new 
man,  and  so  each  half  which  has  resulted  from  this 
first  division  is  in  like  manner  capable  of  developing 
into  a  man.  But,  although  both  of  these  segments 
possess  the  power  to  develop,  only  one  of  them  does 
develop  at  once.  This  one  begins  immediately  to 
undergo  changes  resulting  in  its  speedy  develop- 
ment into  an  adult,  which  we  will  call  the  first  gen- 
eration. The  other  segment,  however,  instead  of 
developing,  remains  unchanged.  It  becomes  in- 
closed in  the  body  of  the  embryo  developing  from 
the  first  segment,  and  there  it  remains  even  after  the 
individual  is  born.  Suppose,  now,  this  individual, 
born  from  the  first  segment,  be  a  female,  the  dor- 
mant segment  finds  its  way  into  the  ovary  of  this 
female,  and  remains  there  as  an  ovum.  Years 
afterward,  when  maturity  is  reached,  and  the  proper 
conditions  present  themselves,  this  ovum  ceases  its 
dormant  condition  and  begins  to  divide,  just  as  did 
the  previous  ovum.  One  half  of  it  develops  into  an 
individual — the  second  generation, — while  the  other 
half  remains  dormant  in  the  body  of  the  second  gen- 
eration, to  develop  in  like  manner  in  its  turn.  And 
so  on ;  half  of  the  ovum  is  carried  over  from  one 
generation  to  the  next.  It  is,  with  this  hypothesis, 
easy  to  see  why  the  second  generation  should  be 
like  the  first,  since  each  is  developed  from  half  the 
same  ovum.  And  so  it  is  just  as  easy  to  under- 
stand why  the  third  generation  should  be  like  the 
first  and  second,  since  all  have  arisen  by  direct  de- 
scent from  the  same  ovum.  Thus  every  generation 


HEREDITY. —  THEORY  OF    WEISMANN.        2/3 

is  like  the  preceding  generation.  This  is  heredity 
according  to  Weismann.  A  child  does  not  inherit 
any  thing  from  its  parents  directly,  but  only  from 
the  ovum.  It  is  like  its  parents  not  because  it  has 
inherited  any  thing  from  them,  but  because  both 
itself  and  its  parents  are  derived  from  half  of  the 
same  ovum,  an  ovum  existing  in  the  body  of  its 
grandparent. 

This  is  of  course  all  hypothesis ;  but  it  is  very 
simple,  and  has  in  its  favor  certain  embryological 
facts.  But  it  will  be  seen  that  it  absolutely  pre- 
cludes the  possibility  of  any  animal  inheriting  any 
thing  directly  from  its  parents,  and  consequently 
acquired  variations  cannot  be  transmitted  to  suc- 
ceeding generations.  According  to  this  view,  every 
child  would  inherit  exactly  the  same  peculiarities 
which  its  parents  inherited,  without  reference  to 
any  features  which  were  developed  in  its  parents  by 
mutilation,  or  use  and  disuse.  Such  acquired  vari- 
ations would  only  affect  the  adult  and  not  the 
ovum,  and  since  the  child  inherits  from  the  ovum 
only  they  could  not  be  inherited.  Weismann  ac- 
cepts this  conclusion,  and  goes  to  some  length  to 
show  that  there  is  really  no  evidence  that  acquired 
variations  are  inherited.  He  says  that  the  only 
variations  which  can  be  inherited  are  variations 
which  affect  the  ovum.  If  this  should  vary  from 
any  cause,  all  individuals  arising  from  it  would  of 
course  show  the  same  results  of  the  variation,  and 
since  all  future  individuals  do  arise  from  this  ovum, 
by  repeated  division,  it  is  evident  that  the  results 
of  an  ovum  variation  would  affect  all  future  genera- 


274  EVOLUTION  OF  TO-DAY, 

tions.  Thus  an  individual,  A,  may  show  in  its  adult 
condition  some  new  feature,  and  its  offspring,  A,1 
may  show  the  same.  The  ordinary  interpretation 
would  be. that  A  transmitted  this  feature  to  A1. 
But  Weismann  would  say  that  the  ovum  from  which 
A  developed  varied  in  such  a  manner  that  this  new 
feature  appeared  in  the  adult.  And  since  A  was 
developed  from  one  half  of  this  ovum,  and  A1  from 
the  other  half,  the  same  feature  would  appear  in 
both,  and  would  then  seem  to  be  transmitted  from 
one  to  the  other.  Weismann  further  believes  that  the 
ovum  is  especially  subject  to  variation,  being  readily 
influenced  by  many  circumstances.  There  are  con- 
stantly arising  variations  which  are  transmitted  from 
generation  to  generation,  but  they  are  all  derived 
from  variations  of  the  ovum  and  never  of  the  adult. 
It  is  evident  that  with  this  explanation  of  heredity 
no  chance  is  left  for  the  inherited  effects  of  use  and 
disuse.  Since  no  acquired  feature  is  inherited,  it 
would  make  no  difference  how  much  an  organ  was  in- 
creasd  by  use  or  diminished  by  disuse;  it  would  have 
no  effect  on  the  next  generation.  Congenital  varia- 
tions alone — /.  e.,  those  arising  in  the  egg — can  be 
inherited.  But  to  accept  this  position  Weismann 
is  obliged  to  explain  away  many  cases  of  well- 
attested  facts.  The  blind  eyes  of  some  animals  is 
only  explained  by  a  loss  of  function  and  size  by  dis- 
use. There  are  a  number  of  cases  on  record  where 
accidental  mutilations  are  inherited,  although  this, 
as  a  rule,  is  not  the  case.  The  numerous  instances 
of  this  kind  are  sufficient  to  show  that  Weismann's 
theory  is  not  wholly  correct.  But  even  more  than 


HAECKEL,  JAGER,  DARWIN.  2/5 

this, — the  only  principle  left  upon  which  Weisman 
can  explain  the  modification  is  selection.  Having 
banished  inheritance  from  parent  to  child,  the  accu- 
mulation of  variations  must  be  by  the  selection  of 
such  chance  varieties  as  appear  in  the  ovum.  Even 
though  it  be  claimed  that  the  ovum  is  particularly 
subject  to  variation,  it  is  plain  that  all  of  the  objec- 
tions urged  against  natural  selection  return  with  re- 
doubled force.  When  in  addition  we  remember 
that  there  is  in  some  cases  positive  evidence  of  the 
inherited  effects  of  use  and  disuse,  it  is  evident  that 
this  theory  of  Weismann  must  be  somewhat  modi- 
fied before  it  can  be  accepted.  It  only  adds  diffi- 
culties to  the  problem  without  removing  them. 
While  it  may  be  that  Weismann  has  found  the  ex- 
planation of  heredity,  he  has  failed  to  find  the  ex- 
planation of  variation. 

Haeckel,  yager,  Darwin. 

A  number  of  other  explanations  of  this  funda- 
mental fact  we  pass  over  with  a  word,  since  they 
only  profess  to  be  explanations  of  heredity,  without 
materially  assisting  toward  the  solution  of  the 
problem  which  we  are  considering — the  modifica- 
tion of  species.  Haeckel  has  a  theory  which  he 
calls  perigenesis,  but  it  is  little  more  than  one  of 
words.  He  thinks  that  the  individual  atoms  of  the 
body  remember.  The  essence  of  his  theory  is  that 
heredity  is  an  unconscious  memory,  the  various 
parts  of  the  body  remembering  the  corresponding 
parts  of  the  ancestor.  This,  with  the  suggestion  that 
reproduction  is  the  transference  of  a  wave  motion 


276  EVOLUTION  OF  TO-DAY. 

from  one  individual  to  another,  something  like  the 
transference  of  fire,  is  his  explanation.  But  this 
is  of  little  assistance.  To  call  a  principle  heredity, 
or  memory,  or  a  wave  force,  gives  about  the  same 
idea  in  any  case  ;  and  no  one  of  them  helps  to  un- 
derstand why  child  is  like  parent. 

Dr.  C.  Jager  has  a  very  different  view.  He  says 
that  all  parts  of  the  body  are  giving  off  from  them- 
selves an  immaterial  essence,  which  he  calls  soul 
stuff.  It  is  this  soul  stuff  which  gives  to  each  ani- 
mal its  own  specific  odor,  and  it  is  different  for  every 
individual.  The  reproductive  products,  he  says, 
collect  this  soul  stuff,  and  store  it  up  in  themselves. 
When  now  these  reproductive  bodies  develop  into 
new  animals,  they  take  the  form  of  the  parents,  since 
they  are  filled  with  a  like  soul  stuff.  The  essential 
feature  of  this  explanation  is  the  supposition  that 
every  part  of  the  body  is  giving  off  from  itself  a 
substance  which  is  transferred  to  the  next  genera- 
tion through  the  ovum  and  the  spermatozoon. 

Darwin  has  also  advanced  an  hypothesis,  which  he 
calls  pangenesis.  He  assumes  that  "the  whole  or- 
ganization, in  the  sense  of  every  separate  atom  or 
unit,  reproduces  itself."  Each  part  of  the  body  is 
constantly  giving  off  from  itself  minute  atoms,  which 
he  calls  gemmules.  These  gemmules  circulate  around 
the  body,  so  that  there  are  present  in  every  part 
millions  of  them,  some  being  present  from  every 
other  part  of  the  body.  When,  therefore,  the  ovum 
gives  rise  to  a  new  individnal,  it  develops  into  the 
parent,  since  it  has  within  it  gemmules  from  every 
part  of  the  body  of  the  parent.  Thus  every  peculi- 


THEORY  OF  BROOKS.  2/7 

arity  of  the  parent,   either  congenital  or  acquired, 
might  be  inherited  by  the  child. 

Theory  of  Brooks. 

A  more  recent  theory  requires  more  extended 
notice,  since  it  not  only  attempts  to  explain  heredity, 
but  also  variation  ;  and  not  only  variation,  but  simul- 
taneous variation  affecting  just  those  parts  which 
need  change.  If  this  theory  can  expain  the  occur- 
rence of  numerous  simultaneous  changes  in  those 
organs  which  need  change,  and  can  demonstrate  the 
inheritance  of  the  effects  of  use,  it  is  plain  that  a 
large  portion  of  the  difficulties  which  have  arisen  in 
the  way  of  all  theories  are  removed.  The  theory  in 
question  is  that  of  an  American  scientist,  Brooks, 
and  is  in  some  respects  a  combination  of  all  the 
others,  but  chiefly  of  the  pangenesis  of  Darwin  and 
the  theory  of  Weismann.  Brooks  takes  into  account 
the  two  sexes,  believing  that  they  have  a  different 
share  in  heredity.  Like  Weismann,  he  explains 
heredity  proper  by  an  appeal  to  the  division  of  the 
ovum.  He  also  would  say  that  early  in  the  devel- 
opment, the  ovum  becomes  separated  into  two 
parts,  one  of  which  develops  into  an  embryo  imme- 
diately, while  the  other  remains  dormant  in  the  ovary 
of  the  developing  individual  until  maturity,  when  it 
in  time  goes  through  its  development.  It  may, 
meantime,  of  itself,  divide  into  many  parts,  each 
like  every  other,  so  that  the  ovary  may  at  maturity 
contain  many  similar  ova.  Heredity  is  then  due  to 
descent  from  the  same  ovum,  and  if  the  ovum  were 
the  only  factor  to  be  considered,  every  child  would 


2/8  EVOLUTION  OF  TO-DAY. 

be  exactly  like  its  parents  and  grandparents.  Thus 
far  the  theory  is  similar  to  that  of  Weismann,  al- 
though Brooks  arrived  at  the  hypothesis  indepen-r 
dently.  To  continue  with  Brooks.  Since,  therefore, 
the  ovum  is  confined  to  the  female  sex,  an  animal 
inherits  from  its  mother  the  characteristics  of  the 
race  which  have  been  long  continued,  and  which  its 
mother  inherited  from  remote  generations.  If  repro- 
duction were  confined  to  the  female  sex,  there  would 
be  no  chance  for  the  inheritance  of  acquired  features. 
(Exceptions  to  this  rule  will  appear  presently.) 
Congenital  variations  might  appear,  but  this  would 
be  all.  Brooks  has  collected  a  large  amount  of  evi- 
dence, which  he  thinks  proves  this  point.  He  finds 
that  in  animals  where  parthenogenesis  occurs,  /.  e., 
reproduction  through  the  female  sex  alone,  there  is 
almost  no  variation,  all  individuals  being  almost 
exactly  alike  for  generation  after  generation.  He 
thinks,  therefore,  that  were  reproduction  confined 
to  the  female  sex,  variations  would  be  comparatively 
rare. 

But  reproduction  is  not  confined  to  the  female 
sex,  and  variation  is,  according  to  Brooks,  due 
chiefly  to  the  influence  of  the  male.  To  explain 
this,  he  supplements  his  theory  with  a  modification 
of  Darwin's  pangenesis.  Like  Darwin,  he  assumes 
that  the  various  parts  of  the  body  are  capable  of 
giving  off  from  themselves  little  bodies  called  gem- 
ules.  But,  instead  of  imagining  them  to  be  scat- 
tered indefinitely  through  the  body,  he  assumes  that 
it  is  the  especial  function  of  the  male  element  to 
collect  them.  The  gemmules  arising  from  the  various 


THEORY  OF  BROOKS.  2?$ 

parts  of  the  body  have  a  tendency  to  accumulate  in 
the  male  generative  organ.  The  spermatozoon  may 
be  regarded  as  a  store  of  these  gemmules.  Now, 
•when  these  spermatozoa  unite  with  the  ovum  in  fer- 
tilization, there  is  introduced  into  the  ovum  a  store 
of  gemmules  from  the  body  of  the  male.  The  intro- 
duction of  such  a  lot  of  new  organisms  into  the 
ovum  must  change  its  constitution,  and  this,  of 
course,  would  cause  it  to  develop  in  a  different 
manner  from  what  it  otherwise  would  have  done. 
In  this  way  is  induced  a  tendency  to  variation  in  the 
offspring  of  sexual  reproduction.  The  ovum  itself 
would  develop  in  the  same  manner  as  did  the  pre- 
vious generation,  but  the  fact  that  it  has  united  with 
the  male  element  of  another  individual  has  intro- 
duced into  it  a  lot  of  new  elements.  These  intro- 
duced gemmules  so  alter  the  ovum  that  it  develops 
somewhat  differently  from  the  previous  generation. 
The  theory  goes  on  to  say  that  these  gemmules  do 
not  affect  the  whole  ovum,  but  each  its  own  special 
part.  Suppose,  for  instance,  that  certain  gemmules 
from  the  parts  of  the  eye  of  the  male  enter  the 
ovum  in  fertilization.  These  gemmules  will  be  at- 
tracted by  some  internal  affinity  to  that  part  of  the 
ovum  which  is  to  give  rise  to  the  eye  of  the  next 
generation,  and  hence  the  eye  will  become  variable. 
So  with  other  parts,  an  internal  affinity  is  supposed 
to  cause  the  gemmules  from  the  different  parts  of  the 
body  to  unite  with  corresponding  parts  of  the  ovum. 
In  this  way  a  child  might  inherit  acquired  variations 
from  its  father,  though  not,  as  a  rule,  from  its 
mother. 


28O  EVOLUTION  OF  TO-DAY. 

It  may  sometimes  happen,  however,  that  gemmules 
arising  in  the  female  might  find  their  way  into  the 
ovum  directly.  If  so,  the  ovum  would  be  directly 
modified  without  the  interference  of  the  male,  and 
an  acquired  variation  of  the  female  would  be  trans- 
mitted. The  male  element  is,  however,  specialized 
to  collect  these  gemmules,  and  therefore  the  varia- 
tions arising  through  the  male  will  be  much  more 
numerous.  Finally,  Brooks  assumes,  and  this  is  the 
important  part  of  the  hypothesis,  that,  although 
every  part  of  the  body  has  the  power  of  giving  rise 
to  these  gemmules,  under  ordinary  circumstances  this 
does  not  occur.  So  long  as  any  part  of  the  body  is 
in  perfect  harmony  with  its  surroundings,  it  simply 
performs  its  functions  without  giving  off  gemmules. 
But  just  as  soon  as  unfavorable  circumstances  occur 
for  the  organ,  gemmules  arise,  which,  finding  their 
way  into  the  male  sexual  bodies,  and  hence  into  the 
ovum,  affect  the  corresponding  organ  of  the  next 
generation.  For  example,  let  us  suppose  some  ter- 
restrial animal  to  change  its  habits  of  life  and  begin 
to  live  in  the  water.  Its  eyes,  which  had  previously 
been  adapted  to  the  air,  are,  of  course,  unfitted  for 
water.  These  unfavorable  conditions  cause  the  ani- 
mal to  strain  its  eyes  in  using  them,  and  this  strain 
causes  the  various  parts  to  throw  off  gemmules. 
These  gemmules  find  their  way  into  the  spermato- 
zoon, and  hence,  at  fertilization,  into  the  ovum. 
Here,  by  their  affinity,  they  affect  that  part  of  the 
ovum  which  is  to  give  rise  to  the  eyes  of  the  next 
generation,  and  this  will  cause  an  immediate  devel- 
opment of  a  large  amount  of  variability  in  the  eye. 


THEORY  OF  BROOKS.  28 1 

Evidently  this  would  happen  to  all  the  offspring  of 
individuals  in  the  same  circumstances.  Many  indi- 
viduals would  thus  vary  simultaneously.  Now, 
natural  selection,  having  simultaneous  variations  to 
work  upon,  may  preserve  the  favorable  varieties 
and  destroy  the  unfavorable.  Every  organ  placed 
out  of  harmony  with  its  environment  will  thus  begin 
to  vary,  and  the  variations  will  appear  where  they 
are  needed.  Moreover,  the  inherited  effects  of  use 
and  disuse  receive  explanation  in  the  same  way ; 
for  an  organ,  used  either  above  or  below  its  normal 
amount,  will  be  out  of  harmony  with  its  conditions, 
and  will  throw  off  gemmules. 

In  a  word,  it  is  from  the  fact  that  a  child  and  its 
mother  are  both  developed  from  part  of  the  same 
ovum,  that  is  due  the  inheritance  of  the  long-con- 
tinued characteristics  of  the  race.  This  is  heredity. 
But  the  origin  of  gemmules,  and  their  introduction 
into  the  ovum  by  fertilization,  cause  the  ovum  to 
become  different  in  its  constitution,  and  the  indi- 
vidual arising  from  it  is  therefore  in  some  respects 
unlike  its  mother.  This  is  variation. 

The  important  features  of  this  theory  are,  first, 
the  claim  that  the  male  is  an  individual  which  has 
become  specialized  for  the  production  of  variation, 
while  the  female  transmits  race  characteristics  ;  and, 
second,  the  claim  that  the  laws  of  the  organism  are 
such  that  variations  appear  in  abundance  in  those 
organs  where  they  are  needed.  The  suggestion  of 
gemmules  is  simply  an  hypothesis  to  explain  these 
two  laws.  It  is  an  important  theory,  because  it  is 
the  first  attempt  to  explain  the  origin  of  simultane- 


282  EVOLUTION  OF  TO-DAY. 

ous  variations  for  successive  generations  in  those 
parts  where  change  is  needed.  If  it  can  be  believed 
that  these  laws  are  real  ones,  it  is  plain  that  a  long 
step  is  taken  toward  the  solution  of  the  problem  of 
the  modification  of  species.  The  various  objections 
urged  against  natural  selection,  from  the  indefinite- 
ness  and  minuteness  of  the  variations,  all  disappear. 
The  views  of  those  who  believe  in  the  great  effect 
of  use  and  disuse  receive  much  support,  and  even 
the  extraordinary  births  of  Mivart  are  somewhat 
more  easily  understood.  This  theory  of  heredity  is 
therefore  an  addition  to  all  of  the  views  we  have 
examined. 

It  would  be  premature  to  attempt  to  draw  any 
positive  conclusion  in  regard  to  this  theory  of 
Brooks.  There  are  certainly  many  objections  which 
arise  and  will  preclude  its  acceptance  in  an  unmodi- 
fied form.  While  it  very  aptly  explains  certain  series 
of  facts,  it  will  not  apply  to  all.  But  that  this  theory 
may  have  reached  one  of  the  important  laws  of 
heredity  seems  highly  probable. 

Summary. 

The  theories  noticed  in  these  two  chapters  are 
not  the  only  ones  which  have  been  advanced  with  a 
like  object,  namely,  to  explain  evolution.  The 
others  are,  however,  of  less  importance,  and  need 
not  detain  us.  It  will  probably  appear  to  many 
readers  that  none  of  them  are  satisfactory,  and  that, 
granting  evolution  to  be  true,  the  explanation  is  not 
yet  fully  obtained,  not  even  by  a  satisfactory  hy- 
pothesis. Let  us  notice  again  the  problem  to  be 


SUMMARY.  283 

solved.  Practically,  all  scientists  accept  evolution 
as  expressing  a  fact  of  nature.  Having  thus  by 
their  theory  eliminated  special  creation  of  species, 
it  becomes  a  logical  necessity  to  show  how  the 
working  of  natural  laws  could  have  produced  an 
evolution.  To  admit  that  the  present  species  are 
descended  from  older  ones  is  no  advantage,  unless  it 
can  be  shown  that  new  species  can  arise  from  old 
ones  by  the  working  of  acknowledged  laws  of  or- 
ganic being.  Two  series  of  facts,  it  is  plain,  must 
furnish  the  data  for  all  explanation  :  heredity  and 
variation.  By  heredity,  species  reproduce  their  own 
kind  ;  by  variation,  they  produce  offspring  some- 
what different  from  themselves.  These  two  series 
of  data  are  not  theoretical,  but  actual.  It  is  a  uni- 
versally recognized  fact  that  animals  and  plants  in- 
herit from  their  parents,  and  it  is  also  universally 
acknowledged  that  they  vary  very  mnch.  Out  of 
these  two  series  of  facts,  then,  must  the  explanation 
arise. 

Darwin  turned  his  attention  to  the  facts  and  selec- 
tion of  variation.  This  subject  he  patiently  studied 
for  many  years,  collecting  a  vast  amount  of  material. 
With  all  his  work  he  was  unable  to  discover  any  im- 
portant laws  which  regulated  the  appearance  of  vari- 
ation. So  irregular  are  they  in  their  appearance,  so 
indefinite  in  direction,  and  so  completely  beyond  the 
realm  of  prediction,  that  he  expresses  his  conclusion 
by  saying  that  organisms  have  an  innate  tendency 
to  vary,  and  that  the  variations  are  chance  varia- 
tions. By  this  he  simply  means,  first,  that  though 
they  all  have  an  efficient  cause,  the  causes  are  com- 


284  EVOLUTION  OF  TO-DAY. 

pletely  hidden  to  the  naturalist ;  and,  second,  that 
they  are  primarily  unrelated  to  any  advantage  re- 
sulting from  them.  They  arise  indefinitely,  and 
some  of  them  chance  to  be  useful.  Darwin  spent 
many  years  in  trying  to  prove  to  himself  and  others, 
that  it  was  the  natural  selection  of  such  chance 
favorable  variations  and  their  transmission  to  suc- 
ceeding generations  that  forms  the  fundamental 
explanation  of  the  gradual  modification  of  species 
and  the  consequent  production  of  new  ones.  He 
admitted  that  other  factors  had  a  certain  though 
subordinate  part,  such  as  use  and  disuse,  or  the 
direct  effect  of  physical  conditions.  He  thought 
that  ornamental  structures  and  sexual  differences 
were  due  to  the  interaction  of  the  sexes.  To  make 
his  theory  complete,  he  forms  an  hypothesis  to  ex- 
plain heredity,  which,  however,  really  forms  no  part 
of  his  general  theory,  and  is  of  little  importance. 
But  aside  from  this,  natural  selection  has  been  found 
inadequate  in  many  other  points,  so  that  even  its 
author,  in  his  later  writings,  was  induced  to  think  it 
of  less  importance  than  he  at  first  believed.  Wag- 
ner suggested  that  species  were  formed  by  isolation 
of  a  few  individuals,  and  this  theory  eventually  led 
him  to  abandon  natural  selection.  Isolation  avoids 
many  difficulties  met  by  the  theory  of  Darwin,  and 
probably  has  had  its  influence.  But  while  isolation 
may  have  been  a  factor  in  many  cases  favoring  the 
modification  of  species,  it  is  impossible  to  believe 
that  all  species  have  arisen  in  this  way.  The  theory 
is  too  small  a  conception  for  the  facts. 

Since   the   simple   selection   of   chance  variation 


SUMMARY.  285 

is  insufficient  to  account  for  evolution,  Nageli 
has  thought  to  help  the  explanation  by  the 
assumption  of  an  innate  tendency  toward  progres- 
sion, which  regulates  the  variations  and  modifi- 
cations of  individuals  in  such  a  way  that  a  con- 
tinual advance  is  the  result.  This  hypothesis  is, 
however,  not  only  uncalled  for  by  the  facts,  but  it  is 
inconsistent  with  some  of  them,  and  it  has  the 
further  disadvantage  of  being  completely  incom- 
prehensible. No  one  can  form  the  slightest  con- 
ception of  what  a  tendency  is  which  may  continue 
to  reside  in  animals  for  millions  of  years,  and  can  be 
transmitted  from  one  generation  to  another.  Al- 
though we  may  doubtless  be  obliged  to  accept  facts 
which  we  don't  understand,  there  is  no  need  of  ac- 
cepting such  a  one  as  this  unless  the  facts  unques- 
tionably demand  it.  Mivart  thinks  that  species 
are  sudden  in  their  appearance,  having  their  origin 
in  extraordinary  births.  He  further  assumes,  as  a 
regulation  of  these  births,  a  unitary  bond  running 
through  nature.  Of  this  bond  he  can  tell  us  nothing, 
not  even  whether  it  is  the  result  of  natural  law  or 
not.  He  would  probably  consider  it  a  supernatural 
bond.  This  view  is  an  evolutionary  one,  since  it 
admits  genetic  descent  ;  but  it  is,  to  a  certain  ex- 
tent, a  view  of  special  creation,  since  it  assumes  that 
each  species  has  had  a  sudden  origin  regulated  by 
some  unknown  force.  Some  American  naturalists 
have  resuscitated  the  old  Lamarckian  theory,  that  it 
is  the  inherited  effects  of  use  and  disuse  which 
contain  the  explanation  sought.  Consciousness  and 
effort  come  in  here  as  an  important  factor.  But, 


286  EVOLUTION  OF  TO-DAY. 

although  the  collateral  evidence  for  this  view  is  not 
wanting,  there  is  some  difficulty  in  getting  direct 
evidence,  since  it  is  even  denied  that  the  effects  of 
use  and  disuse  are  inherited  at  all.  In  order  that 
this  explanation  should  hold,  it  is  therefore  necessary 
to  show  that  such  features  are  transmitted  from  one 
generation  to  another.  It  is  therefore  necessary  to 
study  carefully  the  other  series  of  data  which  we 
have  to  work  with — viz.,  heredity.  In  doing  this 
Weismann  has  found  an  explanation  of  heredity, 
which  causes  him  to  believe  that  the  effects  of  use 
and  disuse  are  not  transmitted.  He  is,  conse- 
quently, obliged  to  fall  back  upon  the  principle  of 
natural  selection  acting  upon  the  variations  of  the 
ovum.  This  view  is  open  to  even  greater  difficulty 
than  that  of  Darwin.  Finally,  Brooks  has  advanced 
a  theory  of  heredity  which,  if  true,  is  of  assistance  to- 
all  of  the  explanations  considered.  By  an  hypothesis 
he  explains  heredity  and  variation.  He  shows  that 
we  may  understand  how  simultaneous  variations  can 
appear  in  such  organs  as  need  change.  The  theory 
thus  offers  to  natural  selection  the  simultaneous 
variations  which  are  necessary.  It  aids  the  theory 
of  Mivart  in  showing  how  extraordinary  births  may 
be  explained,  and  it  is  of  great  assistance  to  the 
Neo-Lamarckian  view,  by  showing  how  the  effects  of 
use  and  disuse  may  be  transmitted  from  father  to 
children.  But,  at  the  same  time,  this  theory  of 
Brooks,  though  valuable,  is  only  an  hypothesis,  and 
many  objections  arise  to  prevent  it  from  being  ac- 
cepted in  its  unmodified  form. 

Perhaps  all  of  the  factors  enumerated  above  have 


SUMMAR  Y.  287 

had  their  influence.  Nature  is  not  a  simple  matter, 
and  there  have  doubtless  been  many  laws  at  work  in 
producing  evolution.  Each  of  our  investigators  has 
probably  discovered  a  truth,  and  each  is  only  in  error 
in  believing  the  law  he  has  discovered  is  of  more 
importance  than  the  others.  Certainly  no  one  of  all 
these  explanations  is  sufficient  to  account  for  the 
question  of  the  origin  of  species.  But  they  are  not 
contradictory,  and  all  may  act  together.  Whether 
with  them  all  it  can  be  believed  that  the  origin  of 
species  is  cleared  up,  it  is  impossible  to  say.  There 
seem  to  be  certain  difficulties  still  existing,  which 
none  of  the  above  suggestions  fully  meet.  But 
neither  of  the  series  of  data,  variation  or  heredity, 
are  yet  fathomed.  Many  laws  have  been  discovered, 
but  there  is  yet  room  for  others.  And  it  is  highly 
probable  that  future  study  of  these  two  subjects  will 
reveal  factors  yet  unthought  of,  which  have  aided  in 
the  origin  of  species.  At  present  it  must  be  ac- 
knowledged that  the  problem  is  not  solved,  even 
though  evolution  be  accepted  as  a  fact. 


CHAPTER  VIII. 

THE   EVOLUTION   OF   MAN. 

THE  question  of  man's  relation  to  the  rest  of  the 
organic  world  has  been  reserved  for  a  special  con- 
sideration, since  in  many  respects  it  stands  by  itself. 
The  subject  is  involved  in  preconceived  notions  and 
sentiments,  and  is  so  plainly  related  to  theological 
ideas,  over  which  discussion  has  always  been  quite 
fierce,  that  the  debates  upon  the  question  are  some- 
what bitter.  Although  in  Darwin's  first  book  noth- 
ing was  said  as  to  man's  origin,  the  tendency  of  his 
theory  was  immediately  perceived.  If  it  had  not 
been  recognized  that  the  first  acceptance  of  evolu- 
tion would  include  the  evolution  of  man  from  the 
lower  animals,  doubtless  the  theory  would  not  have 
been  so  severely  disputed.  But  this  was  recognized, 
and  it  was  soon  definitely  stated  that  man  was  in- 
cluded in  the  scheme.  Darwin  claimed  that  man, 
with  all  his  faculties,  intellectual  and  moral,  had 
been  derived  by  slow  growth  from  the  lower  animals. 
Against  this  conclusion  many  thinkers  have  de- 
murred. The  objections  have  been  due  partly  to  a 
dislike  in  accepting  the  belief.  It  has  been  thought 
to  be  contrary  to  the  teachings  of  revelation,  to  be 
at  enmity  with  a  belief  in  man's  immortality,  etc. 
288 


THE  EVOLUTION  OF  MAN.  289 

These  questions  it  is  not  our  purpose  to  discuss 
here,  beyond  noting  that  many  careful  students  of 
theology  are  of  the  opinion  that  the  ground  is  not 
well  taken.  The  objections  to  the  inclusion  of  man 
in  the  evolutionary  scheme  are,  however,  not  en- 
tirely of  this  character,  many  of  them  being  purely 
scientific  arguments. 

To  the  scientist  who  has  accepted  evolution  in  its 
general  sense  it  seems,  at  first  sight,  hardly  possible 
to  question  the  position  that  man  is  simply  one 
species  of  animals  evolved  in  a  similar  manner  with 
all  others.  Nearly  all  of  the  arguments  which  have 
been  applied  to  the  rest  of  the  organic  world,  as  in- 
dicating evolution,  apply  equally  well  here ;  and  it 
seems  a  matter  of  cowardice  to  exempt  man  from 
the  law.  Of  course,  the  origin  of  man  is  a  matter 
of  more  interest  and  importance  than  that  of  any 
other  animal,  for  it  is  the  question  of  the  origin  and 
destiny  of  man  that  forms  the  most  vital  of  all 
questions  for  study.  But  this  is  no  reason  why  he 
should  not  come  under  the  law  of  evolution.  When, 
however,  the  matter  comes  to  be  examined  care- 
fully, it  is  seen  that  the  questions  of  man's  evolution 
is  quite  a  different  one  from  that  of  other  animals. 
It  has  its  own  special  arguments  and  difficulties. 
It  is  soon  seen  that  evolution  may  be  true  in  regard 
to  other  animals,  and  yet  be  only  partly  applicable 
to  man.  That  this  is  true  is  sufficiently  shown  by 
the  fact  that  several  of  our  best  scientists,  among 
whom  stands  Wallace,  who  shares  with  Darwin  the 
honor  of  discovering  the  principle  of  natural  selec- 
tion, exclude  man  wholly  or  in  part  from  their 


2QO  EVOLUTION  OF  TO-DAY. 

evolutionary  system.     The  argument  is  in  brief  as 
follows : 

Evolution  may  apply  to  all  other  animals,  because 
all  possess  the  same  fundamental  characteristics,  the 
difference  being  only  in  relation  of  parts.  But  man 
is  not  only  an  animal ;  he  is  more.  He  is  an  intel- 
lectual and  moral  being,  and  these  qualities  are  new 
in  kind.  They  are  qualities  which  are  not  repre- 
sented in  animals,  and  could  not,  therefore,  have 
been  derived  from  them.  Just  as  there  is  a  break 
in  continuity  at  the  beginning  of  life,  which  has  not 
been  bridged,  so  here,  at  the  introduction  of  human 
nature,  there  is  another  break.  There  is  much  dif- 
ference of  opinion  as  to  whether  this  argument  is  a 
legitimate  one.  Let  us,  then,  notice  the  position 
held  both  by  those  who  accept  and  those  who  deny 
the  cogency  of  the  argument. 

Mans  Physical  Nature. 

It  may  be  well  at  the  outset  to  acknowledge  that, 
so  far  as  man's  body  is  concerned,  there  is  no  valid 
reason  for  exempting  him  from  an  origin  such  as 
has  been  ascribed  to  the  rest  of  the  organic  world. 
Man  is  just  as  truly  a  member  of  the  vertebrate  sub- 
kingdom,  and  of  the  order  of  primates,  as  is  the 
monkey.  Bone  for  bone,  muscle  for  muscle,  nerve 
for  nerve,  can  his  body  be  compared  with  that  of 
other  vertebrates.  From  this  side  of  his  nature  it 
appears,  according  to  the  best  authority,  that  not 
only  does  man  not  have  a  sub-kingdom  to  himself, 
but  he  does  not  belong  to  a  distinct  order  or  even 
family.  He  forms  simply  a  genus  of  primates 


MAN'S  PHYSICAL  NATURE.  29! 

closely  related  anatomically  to  the  chimpanzee  and 
gorilla.  The  difference  between  man  and  the  apes 
is  anatomically  less  than  that  between  the  ape  and 
the  ordinary  monkey.  It  is  true  that  some  of  the 
older  naturalists  have  attempted  to  make  for  man  a 
distinct  order  of  mammals,  founding  the  distinction 
on  the  size  and  structure  of  the  brain.  This  position 
is  not,  however,  held  to-day.  Man  has  certainly  a 
very  large  brain,  but  it  is  contrary  to  every  principle 
of  nature  to  found  such  distinction  on  a  single  char- 
acter. We  find  organs  present  as  rudiments  in  man 
which  are  well  developed  in  other  vertebrates  ;  or- 
gans developed  as  rarities  in  man  which  are  always 
present  in  certain  other  animals  ;  we  find  the  human 
embryo  developing  in  like  manner  with  other  mam- 
mals, passing  through  the  same  ancestral  stages. 
There  is,  in  short,  nothing  in  the  physical  nature  of 
man  which  exempts  him  from  the  general  principles 
which  regulate  animals.  If  evolution  applies  else- 
where, it  applies  here  also.  When  we  find  man 
agreeing  in  bodily  structure  so  very  closely  with 
other  vertebrates  ;  when  we  find  in  him  rudiments 
of  organs  present  in  the  lower  orders;  when  we  see 
that  the  abnormalities  of  his  body  are  explained  by 
reference  to  other  vertebrates ;  when  we  find  his 
embryology  showing  all  of  the  remarkable  ancestral 
features  seen  elsewhere  ;  in  short,  when  we  see 
that  almost  every  argument  hitherto  used  to  prove 
genetic  descent  in  animals  in  general  applies  equally 
well  to  man,  in  logical  honesty  we  cannot  hesitate 
to  admit  that  if  evolution  exists  elsewhere  it  exists 
here  also. 


2Q2  EVOLUTION  OF  TO-DAY. 

From  geology  there  is  practically  no  evidence 
either  for  or  against  this  view.  Fossil  primates  of 
all  kinds  are  very  rare,  and  fossil  human  remains  are 
rarest  of  all.  In  geological  formations,  which,  it  is 
known,  were  cotemporaneous  with  man,  there  are 
no  traces  of  his  bones.  The  oldest  human  remains 
which  have  been  found  are  certainly  much  more  like 
those  of  the  apes  than  the  man  of  to-day,  particu- 
larly in  the  shape  of  the  skull.  But  these  unques- 
tionably old  skulls  are  so  few  in  number  that  it  is 
impossible  to  draw  any  conclusions  from  them,  par- 
ticularly when  it  is  pointed  out  that  even  to-day 
there  are  occasionally  found  skulls  which  are  about 
as  low  as  these  fossils.  One  point,  however,  geol- 
ogy has  definitely  settled,  and  that  is,  that  man  is  a 
very  old  animal.  Instead  of  existing  only  a  few 
thousands  of  years,  there  is  positive  evidence  that  he 
has  lived  many  thousands.  History  traces  him  for 
about  six  thousand  years,  but  archeology  and  geol- 
ogy carry  him  much  further.  He  has  been  traced 
into  the  early  quaternary  times,  and  some  would 
think  even  earlier.  In  years  it  is  impossible  to  esti- 
mate this  time.  Although  the  tendency  of  recent 
observations  is  to  make  this  time  less  than  was 
formerly  believed,  it  can  hardly  be  possible  that  it  is 
less  than  twenty  thousand  years,  and  probably  much 
more.  But  the  almost  utter  absence  of  bones  either 
of  man  or  of  primates,  makes  it  impossible  to  say 
any  thing  from  this  source  as  to  its  origin.  It  is  un- 
fortunate that  just  where  this  evidence  is  most 
wanted  it  is  lacking,  for  the  absence  of  this  connect- 
ing link  has  been,  and  still  is,  one  of  the  standard 


MAN  AS  AN  INTELLIGENT  ANIMAL.          293 

arguments  against  this  phase  of  evolution.  Your 
primitive  half  man,  it  is  said,  is  only  hypothetical, 
you  cannot  prove  his  existence,  nor  even  find  any 
evidence  of  him  in  fossils.  The  fact  that  the  origin 
of  the  human  race  is  so  much  more  important  than 
that  of  any  other  animal,  makes  this  argument  very 
forcible  in  its  appeal,  and  it  is  sometimes  regarded 
as  insurmountable.  But  as  a  scientific  argument 
this  fact  has  no  more  weight  than  the  absence 
of  certain  other  connecting  links,  of  which  every 
one  admits  there  is  an  abundance.  We  may  be 
more  anxious  in  regard  to  finding  evidence  of  this 
connecting  link  between  man  and  his  supposed  an- 
cestors than  we  are  to  find  evidence  connecting  the 
elephant  with  his  ancestors,  but  we  have  no  more 
reason  for  expecting  the  one  than  the  other.  The 
absence  of  fossil  half-man  is  unfortunate  for  evolu- 
tion, but  it  is  scientifically  only  an  instance  of  the 
imperfection  of  the  fossil  record,  which  we  well 
know  to  be  great. 

Man  as  an  Intelligent  Animal. 

It  is  useless  to  attempt,  as  far  as  man's  body  is 
concerned,  to  exempt  him  from  the  general  principle 
of  evolution,  and  few  would  think  of  doing  so  to- 
day. It  would  be  simply  to  deny  the  cogency  of 
the  arguments  which  are  conceded  elsewhere,  and 
consistency  requires  us  either  to  deny  evolution  al- 
together or  admit  it  here. 

But  when  we  come  to  consider  man  as  an  intel- 
ligent, moral  being,  the  question  assumes  a  very 
different  aspect.  If  man's  mental  qualities  be  taken 


294  EVOLUTION  OF  TO-DAY. 

as  a  basis  for  classification,  he  demands  a  whole 
kingdom  to  himself,  instead  of  a  simple  generic 
rank.  Even  the  lowest  man  is  immeasurably  superior 
to  the  highest  brute.  Between  them  is  a  vast  chasm 
which  no  one  has  yet  been  able  to  bridge.  It  is 
true  that  between  the  lowest  men  and  the  higher 
classes  there  is  perhaps  an  even  greater  difference. 
But  in  this  case  there  is  no  chasm,  for  a  complete 
series  of  higher  and  higher  grades  of  intelligence 
unites  the  two  extremes.  It  is  plain  that  this  differ- 
ence is  one  of  degree,  and  not  one  of  kind.  The 
lowest  men  have  the  same  sort  of  intelligence,  the 
same  kinds  of  emotion,  which  are  found  in  the 
highest  races,  except  that  they  are  less  developed, 
and  turned  into  different  directions.  The  difference 
between  the  intellect  of  a  Newton  and  a  Hottentot 
is  even  greater  than  that  between  the  Hottentot 
and  the  ourang-outang,  but  the  former  difference  is 
filled  by  steps  of  development,  while  the  latter 
difference  is  a  chasm,  seemingly  an  impassable  one. 
Experiment  has  shown  that  a  savage,  if  taken  when 
young  and  brought  up  among  civilized  people,  de- 
velops into  a  very  good  member  of  community, 
about  as  intelligent  as  many  people  among  civilized 
nations.  But  such  an  experiment  would  fail  if  tried 
with  the  ourang-outang.  Here  then,  we  begin  to 
see  the  grounds  for  the  claim  that  man  is  more  than 
animal.  Many  students  hold  the  position  that  in 
regard  to  the  mental  nature — by  this  term  is  meant 
both  intellect  and  moral  nature — the  difference  be- 
tween man  and  the  other  animals  is  one  of  kind,  and 
that  the  chasm  between  man  and  animal  indicates 


MAN  AS  AN  INTELLIGENT  ANIMAL.         295 

that  something  has  been  introduced.  Evidently  if 
these  factors  are  absolutely  new  in  kind,  they  could 
not  have  been  evolved,  for  evolution  does  not  create. 
If  animals  possess  nothing  equivalent  to  this  new 
nature,  man  could  never  have  been  produced  wholly 
by  evolution.  If  this  is  the  conclusion  to  which  we 
must  arrive,  man  must  be  looked  upon  as  something 
different  from  other  animals,  as  a  new  departure. 
Just  what  may  be  meant  by  a  new  departure  is  not 
so  clear.  Perhaps  at  the  appearance  of  man  the 
Creator  implanted  in  him  a  new  spirit,  "  breathed 
into  his  nostrils  the  breath  of  life,  and  man  became 
a  living  soul."  Perhaps  He  so  influenced  some  pre- 
viously existing  animal  as  to  cause  his  development 
in  a  new  direction.  "  An  unknown  cause  accelerated 
the  development,"  says  Wallace.  Either  of  these 
views  would  recognize  the  evolution  of  man,  but 
would,  at  the  same  time,  regard  man  as  more  than 
an  animal,  and  hence  in  a  sense  a  special  creation. 
The  significance  of  either  of  these  two  views  it  is 
not  our  present  purpose  to  discuss.  The  question 
which  we  must  consider  is  one  preceding  this.  Is  it 
necessary  to  assume  that  man  differs  from  animals 
in  any  thing  except  the  degree  of  development  of 
certain  faculties?  Is  the  mental  nature  of  man  such 
in  its  character  that  it  must  be  considered  different 
in  kind  from  that  of  animals?  or  is  it  possible  to  be- 
lieve that  the  intellectual  nature  of  animals  contains 
the  rudiments  of  man's  mental  attributes,  so  that 
human  intelligence,  morality,  etc.,  could  have  been 
derived  by  development  from  that  of  animals  ?  If 
the  former  be  the  truth  it  is  plain  that  there  is  a 


296  EVOLUTION  OF  TO-DAY. 

break  in  the  series  of  continuity.  If  the  latter  be 
true,  then  it  is  possible  that  man  has  been  both 
physically  and  intellectually  evolved  from  lower 
animals.  If  possible,  it  immediately  becomes  prob- 
able from  the  general  lines  of  argument  already  con- 
sidered. 

Method  by  which  the  Evolutionist  Explains  Human 
Intelligence. 

The  evolutionist  has  attempted  the  burden  of 
proof,  and  has  attempted  to  show  that  the  mental 
nature  of  man  could  have  been  derived  by  the 
development  of  the  mind  of  animals.  He  says  that 
man  differs  from  animals  only  in  the  fact  that  his 
intelligence  is  more  highly  developed.  He  even 
goes  so  far  as  to  give  reasons  why  this  intelligence 
was  developed  somewhat  as  follows  :  Every  animal 
must  have  some  means  of  defence  against  its  ene- 
mies. Through  all  the  geological  ages  this  defence 
was  entirely  in  physical  attributes,  in  muscular 
strength,  in  great  size,  and  low  organization  which 
made  great  injuries  possible  without  death.  But 
with  the  advance  in  organization  higher  methods 
of  defence  made  their  appearance.  As  we  have 
noticed  in  considering  paleontology,  there  has  been, 
since  the  tertiary  age,  a  gradual  increase  in  the  size 
of  the  brain,  affecting  all  mammals.  This  increase 
does  not  probably  mean  much  increase  in  intelli- 
gence, but  rather  an  increase  in  the  nervous  control 
over  the  muscles,  and  hence  increased  vigor.  But  it 
was  at  the  same  time  making  a  development  of  in- 
telligence a  possibility.  The  primates  finally  ap- 


METHOD   OF  THE  EVOLUTIONISTS.  2Q/ 

peared  with  a  brain  larger  than  had  before  existed. 
Now,  these  primates  were  endowed  physically  with 
almost  no  means  of  defence,  but,  at  the  same  time, 
they  were  obliged  to  contend  with  many  powerful 
enemies.  To  accomplish  this,  different  courses 
were  taken.  Some  individuals  escaped  their  ene- 
mies by  becoming  arboreal,  and  gave  rise  to  the 
arboreal  monkeys.  But  others  began  to  depend 
for  their  means  of  defence  and  subsistence  upon 
their  superior  cunning.  Thus  intelligence  becomes 
the  most  important  feature  in  development.  The 
brain  has  already  reached  considerable  size,  but  now 
it  rapidly  increases.  Intelligence  comes  in  contact 
with  intelligence,  and  this  is  all  that  is  needed  to 
cause  rapid  advance.  The  contests  of  these  early 
intellectual  beings  with  each  other  is  the  means  of 
continued  advance  in  intellect. 

When  this  intelligence  has  begun  to  contend  with 
intelligence  it  immediately  becomes  the  only  impor- 
tant feature  to  develop.  The  development  of  the 
body  of  this  hypothetical  creature  is  of  little  or  no 
importance.  He  needs  no  natural  weapons,  for  he 
manufactures  artificial  ones  of  more  efficiency.  His 
body  will  therefore  remain  little  changed  except  in 
such  particulars  as  relates  to  his  advance  in  intelli- 
gence. The  continued  use  of  the  hand  causes  it  to 
become  more  delicate ;  the  growth  of  his  brain 
causes  his  skull  to  increase  in  size.  But  except  in  a 
few  such  features  his  body  remains  much  as  it  was. 
While  the  body  remains  practically  stationary,  the 
intelligence  continues  to  advance,  until,  finally,  the 
race  in  question  comes  to  differ  from  its  early  an- 


298  EVOLUTION  OF  TO-DAY. 

cestors,  in  this  respect,  enough  to  make  the  vast 
difference  which  we  see  between  man  and  the  brute. 
Anatomically,  he  has  all  the  time  remained  a  primate, 
but  intellectually  he  has  developed  for  himself  a 
new  kingdom.  Meantime,  all  of  the  intervening 
half-intelligent  animals  have  been  exterminated,  for 
this  animal  will  have  its  severest  contests  with 
others  like  itself.  In  their  contests  all  races  of  less 
intelligent  beings  will  be  blotted  out.  Just  as 
civilization  is  exterminating  savages,  so  savages  in 
their  time  exterminated  earlier  half  intelligent  races. 
Advancing  thus,  and  destroying  all  behind  it,  this 
hypothetical  race  finally  became  man,  with  only  an 
unbridged  chasm  between  him  and  the  brute,  to  in- 
dicate the  road  over  which  he  has  travelled. 

It  would  not,  of  course,  be  claimed  by  evolution- 
ists that  this  was  the  actual  history  of  man,  but 
simply  that  it  illustrates  the  general  line  of  develop- 
ment. Whatever  we  may  think  of  the  sketch,  and 
however  fanciful  it  may  appear,  two  important 
points  are  brought  out  which  are  of  great  moment. 
First,  in  the  minds  of  the  evolutionist,  the  advance 
in  intelligence  from  lower  animals  to  man  has  not 
been  a  continued  one.  Up  to  a  very  late  geological 
age,  when  the  higher  primates  appeared,  intelligence 
was  a  very  secondary  feature  in  development.  The 
lower  vertebrates  differ  not  very  much  from  the 
higher  in  this  respect.  But  the  elements  of  intelli- 
gence were  present  all  of  the  time,  and,  finally,  when 
other  means  of  defence  were  wanting  their  rudiments 
were  unfolded  under  the  influence,  Darwin  would  say, 
of  natural  selection ;  Wallace  would  say,  of  an  un- 


EVIDENCE  FROM  FOSSILS  IS  IMPOSSIBLE.      299 

known  cause  ;  the  Christian  evolutionist  would  say, 
of  God.  Secondly,  the  half-intelligent  races  would 
be  exterminated,  since  they  could  not  contend  with 
the  higher  races. 

Evidence  from  Fossils  is  Impossible. 

Unfortunately  it  is  impossible  from  the  very  na- 
ture of  the  case  to  get  any  evidence  of  the  origin  of 
human  intellect  from  fossils.  Mental  qualities  leave 
no  fossils.  It  is  not  until  mind  is  so  far  advanced 
that  animals  are  able  to  make  artificial  weapons 
or  other  instruments,  that  it  is  possible  for  intel- 
lect to  leave  any  traces  of  itself.  But  when  it 
reaches  this  condition  it  is  human.  And  hence 
the  first  possible  traces  we  can  get  of  mind  is  af- 
ter it  has  reached  the  grade  which  evolutionists  are 
trying  to  explain.  Half-intelligent  man  could  have 
left  no  traces  except  his  bones.  It  is,  however,  sig- 
nificant to  notice  the  character  of  the  earliest  traces 
of  man  which  are  found.  They  consisted  of  the 
rudest  possible  implements  of  stone,  being  noth- 
ing more  than  pieces  of  stone  clipped  in  such  a 
manner  as  to  give  them  a  manageable  shape.  It 
is  impossible  to  conceive  of  any  thing  simpler  which 
would  give  any  evidence  of  mind.  But  the  very 
fact  that  they  do  indicate  mind  shows  that  we  have 
here  evidences  of  men.  From  this  simplest  condi- 
tion archeology  has  been  able  to  trace  a  slow  ad- 
vance in  intelligence.  First,  little  better-shaped 
tools,  still  made  of  stone,  and  then  the  gradual  in- 
troduction of  metal  implements,  more  and  more 
perfect  in  their  shape,  until  historical  times.  Man 


300  EVOLUTION  OF  TO-DAY. 

has,  then,  certainly  developed  from  a  very  low  condi- 
tion. He  cannot  be  traced  back  to  the  animals,  but 
he  can  be  traced  back  to  the  lowest  condition  in 
which  he  could  exist  and  yet  be  a  man.  Earlier 
than  this  evidence  cannot  exist. 

It  must  be  noticed,  however,  that  even  this  conclu- 
sion is  in  part  denied.  The  position  is  held  by  the 
Duke  of  Argyle  and  a  few  others,  that  these  low 
conditions  of  the  human  race  were  not  primitive 
conditions  but  the  result  of  degradation.  Argyle 
would  believe  that  primitive  man  was  neither  the 
lowest  nor  the  highest  race,  but  was  possessed  of 
a  civilization  midway  between  the  two.  He  was 
created  with  human  faculties  well  developed  ;  and 
from  this  primitive  condition  he  has  diverged  in  two 
directions.  On  the  one  hand  advancement  has  led 
to  the  modern  civilized  race ;  while,  on  the  other 
hand,  degradation  has  led  to  the  savage  tribes.  Ar- 
gyle would  not  believe  that  stone  implements  neces- 
sarily indicated  the  primitive  condition  of  man,  but 
rather  a  degraded  condition.  The  reasons  given  for 
this  conclusion  do  not  appear  very  cogent  to  scien- 
tists in  general.  The  chief  argument  seems  to  be 
that  many  of  our  savage  races  to-day  show  evidence 
of  being  degraded  from  a  former  state  of  advance- 
ment. This  fact  can  hardly  be  denied,  and  is  indeed 
admitted  by  all.  But  it  is  far  from  being  sufficient 
to  offset  the  great  weight  of  the  counter  evidence 
obtained  from  the  study  of  archeology.  Among 
scientists  Argyle  stands  almost  alone,  although  Mi- 
vart  holds  a  view  somewhat  similar.  Other  scien- 
tists, however,  believe  that  man  can  be  traced  back- 


INSTINCT  AND  INTELLIGENCE.— EMOTION.      30! 

wards  through  simpler  and  simpler  grades  of 
intelligence  until  the  very  lowest  possible  man  is 
reached,  and  this  man  they  regard  as  primitive. 
Now  it  only  requires  a  little  imagination  on  the 
part  of  the  evolutionist  to  take  one  or  two  steps 
more,  and  man's  body  will  become  ape-like  ;  his  in- 
telligence will  dwindle  away  until  it  is  no  greater 
than  that  of  animals,  and  consequently  all  of  the 
special  human  attributes,  which  depend  on  this 
intelligence,  will  disappear  altogether. 

The  evolutionist  believes,  then,  that  the  human 
mental  nature  is  such  as  could  have  developed  from 
animal  intelligence.  In  order  to  substantiate  this 
claim  it  is  necessary  to  show  one  of  two  things  : 
either  that  all  of  the  qualities  of  human  mental 
nature  are  present  in  animal  minds  in  rudiment  and 
only  require  development,  or  that  they  are  such  as 
can  have  been  developed  from  qualities  which  are 
found  in  animals.  Let  us  now  notice  the  attempt 
which  Darwin  and  others  have  made  to  do  this,  and, 
at  the  same  time,  the  objections  which  their  oppo- 
nents have  raised  against  their  arguments.  The 
force  of  these  arguments  and  objections  is  largely 
a  matter  of  opinion,  and  this  leaves  much  room  for 
dispute.  We  shall  therefore  find  that  almost  every 
position  held  by  either  side  is  combated  by  advo- 
cates of  the  opposite  view. 

Instinct  and  Intelligence. — Emotion. 

A  popular  distinction  between  man  and  animals  is 
that  man  possesses  reason  while  animals  are  provided 
with  instincts.  But  a  very  little  consideration  shows 


302  EVOLUTION  OF  TO-DAY. 

that  this  distinction  is  only  a  relative  one.  In  the 
first  place,  few  would  be  inclined  to  doubt  that  ani- 
mals possess  a  certain  amount  of  reasoning  power. 
At  all  events  this  is  true  if  we  are  allowed  to  use 
the  same  rules  which  we  apply  to  human  actions. 
Animals  certainly  perceive  the  relations  of  means 
to  the  end  in  certain  cases,  and  this,  if  we  can 
judge  from  appearances,  is  reason.  Whether  those 
acts  are  the  results  of  association  of  ideas,  or  of 
a  deeper  reasoning  process,  is  immaterial  at  this 
point.  They  are  at  all  events  not  instinctive.  On 
the  other  hand  man  possesses  instincts.  As  such 
may  be  mentioned  the  actions  of  a  new-born  child 
before  the  slightest  dawn  of  intellect,  sucking,  etc. 
Darwin  also  tells  us,  as  we  shall  see  later,  that  the 
feeling  urging  us  to  do  right  and  avoid  wrong  is 
an  instinct. 

The  chief  authorities  upon  the  matter  of  instinct 
are  Darwin  and  Geo.  Romanes.  They  tell  us  that 
instincts  are  simply  inherited  habits,  and  may,  there- 
fore, be  possessed  by  men  as  well  as  by  animals. 
Animals  acquire  a  certain  habit  either  by  accident 
or  by  intelligence.  If  this  habit  proves  of  use  to 
them  it  will  cause  their  prosperity  and  preservation. 
The  same  habit  will  be  acquired  thus  for  many  gen- 
erations, until  at  last  it  becomes  so  firmly  estab- 
lished in  the  race  that  it  is  transmitted  from  one 
generation  to  another,  and  is,  therefore,  an  instinct. 
That  instincts  may  be  acquired  in  this  manner,  is 
shown  by  the  instinct  of  the  shepherd  dog.  These 
dogs  have  been  taught  to  herd  sheep.  Generation 
after  generation  has  this  habit  been  acquired,  until 


INSTINCT  AND  INTELLIGENCE. — EMOTION.      303 

it  has  finally  become  an  inherited  instinct ;  for  young 
dogs  will  herd  sheep  in  a  proper  manner  the  first 
time  they  are  taken  into  the  pasture.  In  this  case 
the  habit  is  one  which  has  been  taught  the  animal 
by  man.  But  it  is  evidently  possible  that  habits 
which  animals  learn  of  their  own  accord  may,  in  a 
similar  way,  become  instructive.  This,  too,  has  been 
in  many  cases  directly  observed.  After  a  very  ex- 
tended series  of  observations  Romanes  has  con- 
cluded that  this  Darwinian  theory  of  the  origin 
of  instincts  is  perfectly  satisfactory  in  most  cases. 
We  cannot  here  consider  his  arguments  but  only  the 
result.  If  this  conclusion  be  accepted,  it  is  evident 
that  the  difference  between  the  minds  of  men  and 
animals  is  only  one  of  degree,  so  far  as  concerns  the 
possession  of  instinct.  Each  can  acquire  inherited 
habits.  But  in  animals,  owing  to  the  fact  that  the 
general  intelligence  is  small  and  the  reasoning 
powers  almost  absent,  the  instincts  become  the 
factors  of  life.  In  man,  the  development  of  rea- 
son has  caused  instinct  to  become  secondary.  And 
in  most  cases  reason  has  entirely  superseded  instinct 
in  adult  man.  Man  has  discovered  that  reason  is  a 
better  guide  than  blind  impulse — /.  e.,  instinct.  Man's 
mind  is  mostly  intellect  and  little  instinct;  animals' 
minds  are  mostly  instinct  and  little  intellect.  The 
difference  is  certainly  vast.  Whether  or  not  it  is 
more  than  one  of  degree  depends  upon  the  answer 
to  the  question  whether  animal  intelligence  and 
reason  are  similar  in  kind  to  faculties  of  the  same 
name  in  man.  If  they  are,  it  is  plain  that  it  is  only 
necessary  to  suppose  these  qualities,  rudimentary  in 


304  EVOLUTION  OF  TO-DAY. 

animals,  to  develop,  in  order  to  have  an  explanation 
of  the  mental  characteristics  of  man. 

In  the  first  place  it  is  hardly  possible  to  doubt 
that  animals  possess  most  of  the  same  emotions 
which  characterize  man.  Every  one  knows  of  in- 
stances of  love  and  hatred  shown  by  animals  for 
each  other  and  for  man.  A  dog  will  follow  his  mas- 
ter through  every  possible  hardship  ;  is  unhappy 
when  separated  from  him  ;  is  jealous  when  another 
is  petted  in  his  place.  In  what  is  this  different  from 
the  love  which  a  servant  bears  his  master  ?  A  tiger 
will  defend  her  helpless  young  with  her  life.  Is 
this  not  maternal  love  ?  It  does  not  alter  the  facts 
to  claim  that  such  love  on  the  part  of  animals  is  an 
interested  love.  For  human  love  is  in  the  same  way 
influenced  by  circumstances.  A  dog  will  endure  as 
much  ill  treatment  from  his  master  and  yet  retain 
his  love,  as  will  one  human  being  from  another. 
The  significant  fact  is  not  what  may  cause  or  de- 
stroy the  love  of  animals,  but  that,  so  far  as  we  can 
judge,  it  is  love,  similar  to  that  found  in  man.  It  is 
true  that  the  love  shown  by  animals  is  not  of  the 
highest  type,  since  it  never  passes  beyond  love  for. 
friends.  Love  in  man  in  its  highest  sense  is  directed 
also  towards  his  enemies.  But  such  a  feeling  is  sel- 
dom possessed  by  man,  only  the  higher  races  even 
having  a  conception  of  the  idea.  Savages  cannot 
even  understand  it.  The  love  of  animals  is  certainly 
equal  to  that  of  a  child  whose  regard  extends  only 
to  father  and  mother,  and  perhaps  one  or  two  others 
from  whom  it  receives  favors.  If  animals  show  the 
emotion  of  love,  they  also  conceive  hatreds  and  jeaL 


KNOWLEDGE   OF  TOOLS,  ETC.  305 

ousies.  They  possess  the  feeling  of  curiosity  as 
much  as  certain  savage  tribes.  They  have  the 
power  and  habit  of  attention  and  imitation.  They 
certainly  have  memory,  as  is  daily  shown  by  their 
ability  to  learn  and  repeat  tricks.  Who  can  see  two 
kittens  at  play  without  feeling  that  their  emotions 
are  quite  similar  to  those  of  playing  children.  Ani- 
mals have  a  sense  of  beauty ;  witness  the  gorgeous 
display  of  plumage  in  birds  during  the  mating  sea- 
son. Darwin  even  believes  that  animals  possess 
imagination,  which  he  thinks  is  proved  by  their 
dreams.  In  all  of  these  various  respects  then, 
judging  from  their  actions,  animal  minds  are  simi- 
lar to  those  of  man. 

Knowledge  of  Tools,  ete. — Language. — Power  of  im- 
provement.— Consciousness. 

We  now  come  to  certain  qualities  of  man  more 
difficult  to  deal  with  from  the  standpoint  of  the  evo- 
lutionist. And  they  are  points  of  distinction  rather 
than  points  of  likeness  between  the  mental  qualities 
of  man  and  brute.  First,  we  notice  the  frequently 
urged  distinction  that  man  alone  makes  and  uses 
tools,  can  build  a  fire  ;  he  alone  plants  seeds  and 
gathers  the  harvest.  The  position  taken  by  the  evo- 
lutionist on  this  matter  is,  that  these  points  do  not 
indicate  any  new  mental  quality  but  simply  new  dis- 
coveries on  the  part  of  man's  greater  intelligence. 
Animals  understand  the  use  of  tools  and  of  the  fire. 
Every  one  has  heard  of  the  monkey  using  a  stone  to 
crack  nuts,  or  a  stick  as  a  weapon.  The  use  of  tools 
is  a  great  step  toward  their  production.  Evidence 


306  EVOLUTION  OF  TO-DAY. 

in  the  possession  of  archeologists  seems  to  show  that 
the  first  tools  were  simple  stones  which  possessed  a 
peculiar  shape.  From  this  stage  to  their  artificial 
manufacture  is  but  a  step,  provided  we  grant  the 
continual  growth  of  intellect.  Observation  would 
soon  lead  an  intellectual  being  to  discover  that 
plants  came  from  seeds,  and  this  would  lead  to  the 
habit  of  planting  them.  Fire  is  more  difficult  to 
account  for.  It  is  very  difficult  to  see  how  a  half 
intelligent  race  knowing  nothing  about  fire  could 
have  learned  to  produce  it.  But  the  myths  of 
Greece  tell  us  that  at  one  time  man  was  without 
this  servant,  and  that  finally  it  was  stolen  for  him 
from  the  gods  by  Prometheus.  Our  evolutionists  be- 
lieve, therefore,  that  even  this  power  was  a  discovery 
of  man's  growing  intellect,  due  originally,  perhaps,  to 
chance. 

A  somewhat  similar  explanation  is  given  of  the 
possession  of  language.  This  endowment  forms  per- 
haps, the  most  noticeable  distinction  between  man 
and  animals.  There  is  no  doubt  that  every  race  of 
men  has  an  articulate  language,  although  some 
tribes  have  been  considered,  upon  insufficient 
grounds,  to  be  exceptions  to  the  rule.  But  no 
animals  show  any  approach  to  it.  Language  is, 
therefore,  regarded  as  another  discovery  of  advan- 
cing intelligence.  Its  rudimentary  beginnings  Dar- 
win finds  in  the  various  cries  of  animals  expressive 
of  emotion,  such  as  joy,  or  pain.  These  are  not  lan- 
guage, but  may  be  its  foundation.  As  intelligence 
increased,  the  necessity  of  communication  between 
individuals  became  greater.  This  resulted  in  the 


KNOWLEDGE   OF  TOOLS,  ETC.  307 

first  attempts  to  associate  sounds  or  signs  with 
objects.  Once  begun  in  this  way,  the  possession  of 
language  would  rapidly  increase  the  development  of 
intellect,  and  this  would  react  upon  language.  The 
two  would  thus  develop  side  by  side.  This  conclu- 
sion is  substantiated  by  philologists,  who  have  studied 
the  matter  from  an  entirely  different  standpoint  and 
for  a  different  purpose.  Foremost  among  them  may 
be  mentioned  our  own  Whitney,  who  has  reached 
the  conclusion  that  the  origin  of  language  has  been 
one  of  growth  and  development.  Language,  he 
has  concluded,  was  at  first  very  simple,  consisting 
of  only  a  few  words,  expressive  probably  of  emo- 
tions. The  origin  of  these  words  is  not  clear,  but 
they  came  as  soon  as  intellect  needed  them.  Some 
perhaps  were  imitations  of  certain  sounds ;  more 
were  probably  arbitrary  association  of  words  with 
definite  ideas.  Original  language,  he  tells  us,  was 
largely  assisted  by  signs.  In  some  simple  way  man 
contrived  to  communicate  with  his  fellow  as  soon  as 
he  became  intelligent  enough  to  have  any  thing  to 
communicate.  Language  is  thus  a  necessary  con- 
comitant of  intelligence.  Darwin  is  thus  strongly 
supported  in  his  theory  of  language,  by  those  who 
have  made  it  a  life  study ;  for  this  conclusion  is  now 
almost  the  universal  consent  of  leading  philologists. 
Language  is  thus  only  a  tool  which  man  has  fash- 
ioned for  his  use,  and  indeed  the  most  important 
one  he  has  made.  It  is  something  new,  and  even 
new  in  kind,  but  it  is  not  a  mental  endowment.  It 
is  a  manufactured  article,  which  man  has  made  as 
he  needed  it.  If  it  be  conceded  that  intelligence  in 


308  EVOLUTION  OF  TO-DAY. 

general  could  have  been  derived  from  animals  by 
development,  language  presents  no  difficulty.  Lan- 
guage is  impossible  without  a  considerable  degree  of 
intelligence,  and  intelligence  is  impossible  without 
language.  Each  has  been  the  result  of  a  slow 
growth. 

Great  stress  has  been  laid  upon  consciousness  as  a 
distinctive  factor  of  the  human  intelligence  as  com- 
pared with  that  of  the  brute.  But  it  is  hardly  neces- 
sary to  say  that  nothing  is  known  about  this  factor. 
We  know  that  we  possess  consciousness,  but  we 
know  nothing  as  to  this  in  animals.  Memory  cer- 
tainly implies  a  certain  amount  of  consciousness, 
and  animals  possess  memory.  There  is  about  as 
much  evidence  for  its  existence  in  some  animals  as 
in  some  people.  Consider,  for  instance,  a  low 
savage  woman  whose  sole  thoughts  in  life  are 
eating,  sleeping,  and  producing  children.  She  gives 
no  evidence  of  any  consciousness  beyond  that  of 
existence,  which  even  dogs  possess.  Evolutionists 
tell  us,  too,  that  it  is  no  more  difficult  to  say  when 
consciousness  comes  into  the  human  race  than  to 
say  when  it  is  developed  in  the  child.  The  infant 
has  certainly  less  consciousness  than  animals,  and 
no  one  can  say  when  it  appears  in  life.  Just  as  it 
develops  in  the  child  as  a  result  of  contact  with  the 
world,  so  it  has  developed  in  the  human  race.  Here, 
again,  development  is  a  repetition  of  past  history. 

Very  much  stress  has  been  laid  upon  man's  power 
to  improve,  for  here  does  a  difference  between  man 
and  the  brute  manifest  itself  in  a  remarkable  man- 
ner. Unlimited  power  of  improvement  in  man,  and 


KNOWLEDGE   OF  TOOLS,  ETC.  309 

no  power  of  improvement  in  animals,  would  cer- 
tainly imply  as  radical  a  distinction  as  it  is  possible 
to  conceive.  But  neither  of  these  two  statements 
is  correct,  and  here,  too,  it  is  claimed  the  differ- 
ence is  one  of  degree.  On  the  one  hand,  animals 
certainly  have  some  power  to  improve.  For  instance, 
the  dog  is  usually  regarded  as  the  most  intelligent 
animal,  and  compared  with  the  wolf,  from  which 
our  dogs  have  probably  descended,  his  intelligence 
is  very  great.  It  is,  therefore,  highly  improbable 
that  when  first  domesticated  dogs  were  as  intelli- 
gent as  they  are  now.  They  have  probably  in- 
creased their  mental  power  owing  to  contact  with 
man.  Or  even  better  is  this  possibility  shown 
by  a  gradual  improvement  of  certain  instincts. 
It  has  been  observed  that  birds  have  within  a 
few  years  improved  their  method  of  nest-building. 
On  the  other  hand,  the  unlimitedness  of  man's  power 
to  improve  is  even  more  questionable.  Of  the  limit 
to  the  improvement  of  the  race  we  can,  of  course, 
know  nothing  as  regards  either  man  or  animal ;  but 
the  limit  of  improvement  in  the  individual  is  soon 
reached.  An  illustration  will  best  indicate  the  evo- 
lutionist's position  on  this  point.  If  a  new-born 
chimpanzee  be  compared  with  the  child  of  a  negro 
and  of  a  white  man,  at  the  same  age,  little  difference 
will  be  seen  between  them  so  far  as  intellect  is  con- 
cerned. If  any  thing  it  will  be  in  favor  of  the  ape. 
Compared  again  in  a  few  months,  the  ape  will  be 
found  to  have  distanced  the  other  two.  But  now 
the  mental  development  of  the  ape  becomes  slower, 
and  stops  ;  while  the  two  human  children  soon  catch 


3IO  EVOLUTION  OF  TO-DAY. 

up  with  him.  The  ape  can  even  after  this  be  taught 
to  do  many  things  by  imitation,  but  he  becomes 
thereby  no  more  intellectual.  The  two  human  chil- 
dren go  on  for  some  years,  when,  as  a  rule,  the  men- 
tal growth  of  the  negro  stops.  He  can  also  be  still 
taught  many  things,  but  he  is  merely  receptive  and 
not  creative.  The  white  child  continues  the  unfold- 
ing of  his  mental  powers  for  some  time  longer,  but 
eventually  he  reaches  a  limit,  at  an  age  varying  with 
different  persons.  Some  reach  their  intellectual 
growth  by  their  fifteenth  year,  others  even  earlier, 
while  others  still  continue  their  mental  unfolding  for 
twenty,  thirty  years,  or  even  more.  By  intellectual 
advance,  it  will  be  understood,  is  not  meant  the  ac- 
cumulation of  facts  of  knowledge,  but  the  growth  of 
mental  powers.  A  study  of  our  public  schools  reveals 
the  significant  fact  that  from  the  time  the  students 
enter  the  high  school,  one  by  one  they  seem  to 
reach  the  limit  of  their  advance.  With  such  facts 
does  it  appear  that  even  this  distinction  is  one  of 
degree.  Man  has  simply  carried  the  limit  of  his 
advance  higher. 

The  various  suggestions  above  enumerated  were 
offered  chiefly  by  Darwin  to  explain  the  facts  in 
question.  By  some  they  are  regarded  as  sufficient. 
But  by  others  they  are  considered  insufficient  to  ex- 
plain all  that  is  claimed  for  them.  Against  each 
position  we  find  objections  urged  from  various 
sources.  But  since  all  these  objections  are  sub- 
sidiary to  the  general  argument  of  those  who  deny 
Darwin's  position,  we  will  not  stop  to  consider  them 
here. 


ABSTRACT  IDEAS.  311 

Abstract  Ideas. — Idea  of  Causation,   Time,  and 
Space,  etc. 

Finally,  we  come  to  certain  qualities  which  consti- 
tute the  essence  of  the  human  intellectual  process. 
Foremost  among  them  stands  the  moral  nature  of 
man.  Of  no  less  importance  is  his  power  of  forming 
abstract  ideas  and  thus  classifying  thoughts.  Here, 
too,  are  found  various  intuitions,  time,  space,  the 
idea  of  force,  of  causation,  etc.  It  is  at  these  points 
that  those  who  believe  man  to  be  a  distinct  creation, 
in  any  sense,  rest  the  force  of  their  argument.  Un- 
less the  origin  of  these  factors  is  explained,  the 
whole  argument  of  Darwin  as  to  man  is  worth- 
less ;  for  they  are  the  really  essential  parts  of  hu- 
man intellect.  I  have  neither  the  knowledge  nor 
the  inclination  to  deal  with  these  questions,  except 
in  a  very  superficial  manner.  They  belong  rather 
to  mental  philosophy  than  science.  Nor  is  it  par- 
ticularly desirable  to  do  much  more  than  state  the 
positions  held  by  different  thinkers,  since  the  con- 
clusion which  one  forms  is  little  more  than  a  matter 
of  opinion. 

The  power  of  forming  abstract  ideas  is  one  of  the 
most  important  possessed  by  man.  Human  thinking 
consists  in  analyzing  and  classifying  ideas,  and  with- 
out this  power  thought  is  impossible.  From  con- 
crete objects  man  forms  abstract  ideas  :  he  com- 
bines and  classifies  them,  studies  their  relations,  and 
reaches  other  abstract  ideas  as  conclusions.  This 
is  thought.  Even  language  is  impossible  without 
these  ideas,  for  language  is  the  association  of  sounds 
with  ideas  and  not  with  objects.  It  is  perfectly  evi- 


312  EVOLUTION  OF  TO-DAY. 

dent  that  no  language  is  possible  until  intelligence 
has  reached  a  condition  where  it  can  conceive  ab- 
stract conceptions.  It  is  almost  equally  evident 
that  as  soon  as  this  condition  is  reached  language 
will  appear.  Here,  then,  is  a  fundamental  condition 
of  the  mental  life,  of  man.  Can  this  factor  or  its  ru- 
diment be  found  in  animals  ?  Darwin  is  inclined  to 
think  so.  A  dog,  he  says,  seeing  another  in  the  dis- 
tance recognizes  it  immediately  as  a  dog.  Upon  com- 
ing closer  he  perceives  it  to  be  a  particular  friend  or 
foe.  The  two  conceptions,  Darwin  says,  are  very  dif- 
ferent. If  the  dog  had  language  he  would  have  one 
sign  for  dog  in  general,  and  another  for  a  particular 
friend.  Or,  again  :  a  man  takes  his  gun  and  calls  his 
dog,  when  the  dog  immediately  perceives  that  they 
are  going  to  hunt,  an  idea  of  a  class  and  not  of  a  con- 
crete object.  A  few  such  instances  as  these  consti- 
tute the  only  evidence  of  this  power  in  animals. 
But  few  will  believe  that  this  is  sufficient  to  be 
regarded  as  a  beginning  of  this  fundamental  factor 
of  human  thought.  It  is  even  improbable  that  any 
thing  like  an  abstract  idea  is  formed  in  these  cases. 
Association  is  a  simpler  and  equally  probable  ex- 
planation. The  sight  of  a  dog  recalls  by  association 
other  concrete  dogs.  The  sight  of  the  gun  in  the 
master's  hands  recalls  the  former  pleasures  of  the 
chase,  without  any  necessity  of  the  idea  of  chase  in 
general.  The  conclusion  here  is  little  more  than  a 
matter  of  opinion.  Darwin,  who  has  chiefly  studied 
animals,  and  who  accepts  from  general  grounds  the 
evolution  of  man,  believes  such  instances  sufficient 
to  indicate  in  animals  the  rudiment  of  the  power  of 


ABSTRACT  IDEAS,  313 

forming  abstract  concepts.  Others  who  have  chiefly 
studied  human  mind,  deny  that  these  instances  can 
be  regarded  as  a  sufficient  foundation  for  this  funda- 
mental quality. 

And  thus  with  the  idea  of  causation.  The  con- 
ception  that  every  thing  must  have  an  adequate 
cause,  is  a  universal  factor  of  the  human  mind. 
Even  the  lowest  savages  have  the  conception,  as  is 
shown  by  their  assuming  the  existence  of  numerous 
gods  to  explain  natural  phenomena.  Yet  this  is  not 
the  result  of  observation.  We  perceive  sequence  of 
events,  but  never  causation.  The  idea  that  one  has 
caused  the  other  is  a  necessity  of  thought,  not  of 
facts.  It  is  indeed  a  law  of  human  thought,  and  is 
the  basis  of  true  reasoning.  But  no  one  has  ever 
been  able  to  find  any  evidence  of  its  existence  in 
animals,  and  it  is  extremely  improbable  that  they 
have  the  slightest  conception  of  any  thing  more 
than  sequence.  Even  in  the  human  race  this  idea 
only  comes  with  a  certain  maturity  of  intellect,  and 
it  is  impossible  to  believe  that  animals  possess  this 
quality  while  children  do  not.  If  animals  do  not 
have  this  concept,  it  follows  that  true  reasoning  is 
impossible  for  them,  and  that  what  seems  to  be 
reason  is  simple  association  of  ideas.  In  the  same 
way  the  conceptions  of  time  and  space  are  neces- 
sary laws  of  thought,  and  not  the  result  of  observa- 
tion. They  constitute  part  of  the  data  of  thinking. 
It  is,  of  course,  impossible  to  deny  positively  that 
they  may  not  be  present  as  rudiments  in  animals, 
but  it  is  equally  impossible  to  find  any  evidence  of 
them.  Here  again  it  is  a  matter  of  opinion  whether 


314  E  VOL  UTION-  OF  TO-DA  Y. 

it  be  necessary  to  find  more  traces  of  these  intuitions 
in  animals  in  order  to  make  the  evolution  of  mind  a 
possible  belief. 

Moral  Nature. 

A  more  extended  consideration  is  required  of  the 
moral  nature  of  man.  This  phase  of  man's  nature 
is  the  most  important  of  all,  and  has  taken  the  most 
prominent  position  in  all  discussions  as  to  the  rela- 
tion of  man  to  the  lower  animals.  More  than  any 
other  subject  has  this  question  been  open  to  the 
odium  theologicum  and  odium  anti-theologicum,  and 
the  discussion  has  ofttimes  been  more  bitter  and 
dogmatic  than  candid  and  logical.  Frequently  it  is 
difficult  to  see  what  the  various  disputants  are  try- 
ing to  prove.  It  is  plainly  evident  that  this  factor 
of  man's  nature  must  be  explained,  or  the  whole 
argument  is  valueless. 

First,  a  word  as  to  the  various  phases  of  the  moral 
nature  comprised  under  the  terms  religion,  reverence 
for  God,  a  belief  in  the  supernatural,  a  belief  in  im- 
mortality, etc.  All  of  these  factors  are  almost  uni- 
versally present  in  men.  Almost  universal,  but 
probably  not  quite,  since  a  few  savage  tribes  seem 
to  be  lacking  in  any  ideas  of  this  kind.  To  be  sure, 
it  is  almost  impossible  to  say  positively  that  this  is 
so.  Our  only  information  must  be  derived  from 
travellers,  and  they  are  very  apt  to  be  deceived,  as  is 
shown  by  the  different  conclusions  different  travel- 
lers have  reached  in  regard  to  the  same  tribes.  It  is, 
however,  the  general  belief  of  ethnologists  that  some 
few  tribes  are  utterly  devoid  of  any  idea  of  the 


MORAL  NATURE.  315 

supernatural.  But  this  is  of  little  importance,  for 
the  fact  still  remains  that  the  human  race  is  charac- 
terized by  these  beliefs,  even  though  some  few  de- 
graded tribes  have  lost  them. 

We  are  told  by  Spencer  that  such  beliefs  have  had 
a  purely  natural  origin.  A  belief  in  life  after  death 
arose  from  dreams,  in  which  those  who  had  died  re- 
appeared to  their  friends.  Primitive  man,  knowing 
nothing  of  the  nature  of  dreams,  naturally  concluded 
that  his  friends  were  still  in  existence  and  had  re- 
turned to  him.  A  belief  in  the  supernatural  arose 
from  the  attempt  to  find  an  explanation  of  natural 
phenomena.  Every  phenomenon  which  was  not 
understood  must  have  been  caused  by  some  power, 
and  these  unknown  powers  were  the  gods  of  prime- 
val man.  Religion  was  simply  the  attempt  to  pro- 
pitiate these  unknown  powers  by  offerings.  The 
feeling  of  reverence  is  only  such  feeling  as  any 
animal  feels  before  beings  which  he  acknowledges 
superior  to  himself.  It  is  closely  akin  to  the  feeling 
which  the  dog  has  for  his  master,  if  not  identically 
the  same.  All  of  these  beliefs  and  feelings  are  thus, 
according  to  this  evolution  school,  simply  the  result 
of  man's  inability  to  explain  the  world  around  him. 

But  the  important  factor  of  the  moral  nature  is 
quite  different  from  any  of  these.  It  is  what  is 
known  as  moral  sense,  or  conscience.  This  is  the 
factor  in  his  nature  which  causes  him  to  distinguish 
between  a  right  and  a  wrong.  This  law  of  thought 
is  unique.  It  stands  at  the  foundation  of  all  codes 
of  morals,  and  upon  our  belief  as  to  its  origin  will 
depend  our  whole  conception  of  human  nature. 


3 1 6  E  VOL  UTION  OF  TO-DA  Y. 

In  the  first  place  it  must  be  noticed  that  this 
moral  sense  is  a  universal  possession  of  mankind. 
There  is  no  race  so  low  as  to  be  devoid  of  con- 
science. But  just  here  has  arisen  a  misunderstand- 
ing. The  intuitionalist,  seeing  this  universal  factor, 
claims  that  all  men  are  born  with  the  intuition  of 
right  and  wrong;  meaning  by  this  an  intuition  of  a 
difference  between  right  and  wrong.  But  many 
scientists  imagine  that  this  claim  is  that  men  are 
born  with  a  knowledge  of  right  and  wrong  actions. 
They  think,  therefore,  if  they  can  show  that  differ- 
ent people  have  different  ideas  as  to  right  and 
wrong,  they  have  disproved  the  claim.  Now  every 
one  knows  that  different  races  have  different  codes 
of  morals.  It  is  possible  to  find  races  of  men  who 
consider  as  praiseworthy  acts,  those  which  we  look 
upon  as  the  greatest  crimes.  Cruelty,  dishonesty, 
theft,  murder,  are  all  believed  by  some  people  to  be 
deeds  of  great  merit.  On  the  other  hand,  acts 
which  we  consider  of  no  importance  whatever  are 
by  some  races  looked  upon  as  crimes.  Moreover 
there  has  been  a  gradual  development  of  our  moral 
nature.  Civilized  man  is  much  higher  in  the  grade 
of  morals  to-day  than  he  was  a  few  centuries  ago. 
Not  many  generations  ago  our  forefathers  consid- 
ered it  a  duty  to  burn  the  Salem  witches ;  but  we 
recall  such  acts  with  horror,  and  would  consider 
them  not  only  barbaric  but  wrong.  Thus  from  the 
earliest  times  there  has  been  a  constant  growth  of 
morals.  Now  there  are  many  who  think  that  such 
facts  as  these  prove  that  the  moral  sense  is  not  alike 
in  all  men.  As  soon  as  this  is  admitted  the  signifi- 
cance of  the  intuitionalist's  argument  is  lost. 


MORAL  NATURE.  317 

But  this  rests  upon  a  complete  misunderstanding 
of  the  subject.  All  of  this  sort  of  argument  is 
interesting  and  valuable,  since  it  indicates  the  devel- 
opment of  our  ideas  as  to  what  is  right  and'what  is 
wrong.  But  instead  of  showing  the  moral  sense  to 
be  different  in  different  people,  it  proves  its  univer- 
sal existence.  No  intuitionalist  even  for  a  moment 
pretended  that  men  are  born  with  a  knowledge  of 
right  and  wrong  acts.  The  point  is  not  that  all  men 
believe  the  same  things  to  be  right  or  wrong,  but 
that  all  men  believe  something  to  be  right.  No 
matter  how  differently  conditioned  be  the  races  of 
men,  no  matter  how  diverse  their  ideas  as  to  right 
and  wrong  actions,  every  person  believes  that  there 
are  some  things  right  to  do  and  some  things  wrong 
to  do.  A  right  and  a  wrong  exist  for  every  race, 
and  the  imperious  word  ought,  is  everywhere  under- 
stood. It  makes  no  difference  to  what  specific  acts 
men  apply  these  terms  so  long  as  they  apply  them 
at  all,  and  recognize  that  those  things  which  they 
consider  right  ought  to  be  done.  Nor  does  it  make 
any  difference  here,  how  we  attempt  to  account  for 
the  reason  for  doing  right.  It  is  a  widespread  con- 
ception that  we  are  to  be  punished  for  wrong-doing 
either  spiritually  or  temporarily.  Students  of  eth- 
ics tell  us  that  it  is  necessary  to  assume  some  ulti- 
mate good  as  the  final  justification  of  Tightness. 
Now  this  may  indeed  be  of  importance  when  we 
consider  the  origin  of  this  moral  sense,  but  it  has  no 
significance  in  considering  its  existence.  People 
throughout  the  world  act  in  certain  ways  because 
they  feel  it  is  right,  and  not  because  they  feel  it  to 


318  EVOLUTION  OF  TO-DAY. 

be  for  their  greatest  happiness.  It  is  only  the 
higher  classes  who  ever  think  of  these  questions. 
The  vast  majority  never  ask  what  the  meaning  of 
right  is,  beyond  that  it  is  something  that  must  be 
done. 

Understanding  then  what  is  meant  by  moral 
sense,  it  cannot  be  claimed  that  there  is  any  race  of 
men  destitute  of  it.  Some  may  have  a  greater 
development  of  this  sense  than  others.  Some  may 
scarcely  feel  any  uneasiness  at  any  amount  of  crime ; 
some  may  feel  uncomfortable  from  wrong-doing; 
some  may  feel  repentant,  and  some  may  feel 
remorse,  over  some  very  trifling  misdeed.  Some 
may  have  so  far  disregarded  this  feeling  that  it  has 
almost  disappeared.  There  has  been  and  still  is  a 
continual  growth  in  the  application  of  this  principle 
to  concrete  instances,  leading  to  a  development  of 
morals.  There  are  as  many  different  codes  of 
morals  as  there  are  races  of  men.  But  no  race  con- 
founds the  ideas  of  right  with  any  thing  else,  and 
every  savage  distinguishes  between  right  and  ex- 
pediency. 

This  being  recognized,  the  next  question  to  con- 
sider is  whether  there  is  any  thing  corresponding  to 
a  moral  sense  in  animals.  This  question  is  a  diffi- 
cult one  to  answer,  but  it  will  usually  be  decided  in 
the  negative.  It  is  a  well-known  fact  that  some 
animals,  particularly  dogs,  can  be  taught  to  refrain 
from  certain  acts.  Even  in  the  absence  of  their 
master,  they  remember  the  prohibition,  and  exhibit 
shame  when  caught  in  doing  those  things  which  are 
prohibited.  This  certainly  resembles  a  sense  of 


MORAL  NATURE.  319 

right  and  wrong.  But  there  is  an  important  differ- 
ence. No  animals  ever  developed  this  quality  spon- 
taneously, for  it  must  always  be  taught  to  them  by 
man,  and  it  is  found  only  in  exceptional  cases.  But 
it  is  universally  present  in  man,  and  since  he  is  the 
highest  animal,  he  must  either  have  developed  it 
himself  or  have  received  it  from  some  superior  being. 
We  send  missionaries  to  the  savages,  but  no  one  ever 
conceived  the  idea  of  sending  them  to  a  zoological 
garden.  If  then  our  evolutionist  is  looking  for  the 
equivalent  of  the  moral  sense  in  animals,  he  must  look 
for  it  among  the  qualities  which  they  have  developed 
spontaneously.  Now  we  do  find  habits  among  ani- 
mals somewhat  difficult  to  understand.  They  care- 
fully protect  their  young,  they  frequently  will  de- 
fend each  other  when  attacked,  they  sometimes, 
though  not  frequently,  care  for  the  injured  ;  they 
warn  each  other  of  danger,  and  assist  each  other  in 
various  ways.  All  such  actions  are  regarded  in  man 
as  praiseworthy,  but  certainly  not  as  moral.  It  is  of 
course  impossible  to  say  just  what  may  be  the  feel- 
ings of  a  dog  who  risks  and  loses  his  life  in  rescuing 
his  master.  Very  likely  they  are  similar  to  those  of 
a  man  who,  upon  a  sudden  impulse,  risks  his  life  to 
save  a  person  from  a  burning  building.  Neither  act 
would  be  moral,  for  its  opposite  would  not  be  wrong. 
But  both  would  be  heroic.  Most  people  will  not 
regard  any  of  these  actions  on  the  part  of  animals 
as  in  any  sense  equivalent  to  moral  actions  in  man. 
The  Darwinian  school,  however,  as  we  shall  presently 
see,  does  regard  them  as  similar,  both  in  their  nature 
and  origin. 


320  EVOLUTION  OF  TO-DAY. 

At  all  events  here  is  a  factor  to  be  explained.  A 
moral  sense  has  been  universally  developed  by  man, 
and  its  existence  in  animals  is  more  than  question- 
able. This  seems  a  very  little  matter,  the  simple 
ability  to  distinguish  between  right  and  wrong,  but 
it  is  in  reality  the  foundation  of  the  whole  moral 
nature.  Is  it  possible  to  give  a  natural  explanation 
of  this  quality  of  the  human  mind  ?  Can  any  process 
be  discovered  by  which  the  ordinary  relations  of 
animals  could  ever  have  given  rise  to  the  conception 
of  right  as  something  which  ought  to  be  done  at 
whatever  sacrifice,  and  wrong  as  something  which 
ought  never  to  be  done  whatever  the  seeming  good  ? 
Here  we  find  a  most  serious  disagreement  among 
thinkers.  On  the  one  hand  stand  the  extreme  evolu- 
tionists, foremost  among  whom  are  Mill,  Darwin, 
and  Spencer,  who  claim  that  this  moral  sense  is 
nothing  more  than  a  modified  form  of  animal  in- 
stinct, and  has  been  developed  through  natural 
causes.  On  the  other  hand  are  many  thinkers, 
among  scientists  Wallace,  Mivart,  Argyle,  Quatre- 
fages,  most  all  theologians,  and  the  intuitional 
school  of  philosophers  in  general,  who  deny  the  posi- 
tion of  the  evolutionist  in  entirety,  claiming  that  no 
case  has  been  made  out,  and  that  the  whole  question 
as  argued  from  the  standpoint  of  the  evolutionist  is 
misunderstood.  Let  us  first  notice  the  Darwinian  the- 
ory, as  an  illustration  of  the  evolutionist's  standpoint. 

Darwin's  Explanation  of  the  Origin  of  the  Moral  Sense. 

The  foundation  of  this  explanation  is  the  fact  that 
any  line  of  action  to  be  morally  right  must  result  in 


THE  MORAL   SENSE.  $21 

some  good.  This  point  is  universally  agreed  upon 
by  all  schools,  though  there  is  the  widest  difference 
of  opinion  as  to  what  this  good  may  be.  Some 
would  call  it  a  happiness,  some  pleasure,  to  the  in- 
dividual ;  some  would  say  it  is  the  good  of  the  race, 
or  the  tribe ;  some  that  it  is  the  greatest  good  to 
the  greatest  numbers ;  some  would  say  it  is  the 
good  of  both  the  individual  and  the  race ;  some  re- 
gard it  as  temporal,  some  as  eternal,  happiness.  But 
though  varied  in  their  idea  of  good,  all  justify  the 
Tightness  of  actions  by  their  producing  more  good 
than  their  opposite.  That  this  is  so,  will  be  evident 
by  supposing  that  something  now  considered  a  crime 
should  be  found  to  be  for  the  permanent  good  of 
the  world,  when  it  would  cease  to  be  a  crime,  and 
be  regarded  as  a  meritorious  action.  Murder  is 
believed  to  be  wrong,  yet  most  persons  will  consider 
the  execution  of  criminals  right  if  it  be  productive 
of  the  best  results. 

Starting  now  with  this  principle,  that  any  action 
to  be  morally  right  must  be  productive  of  good,  it 
is  claimed  that  the  habit  of  regulating  life  by  right 
actions  would  be  gradually  developed  by  natural 
selection.  All  animals  have  instincts  and  impulses 
of  various  kinds,  some  of  which  are  of  use  and  some 
of  which  are  doubtless  of  direct  injury.  For  the 
bird  who  cannot  endure  the  rigor  of  a  northern 
winter,  the  instinct  to  migrate  is  doubtless  of  great 
importance.  In  a  modified  sense,  therefore,  the 
bird  ought  to  migrate.  Now,  of  these  various 
instincts,  some  are  stronger  than  others,  so  that 
when  they  come  in  contact  the  stronger  ones 


322  EVOLUTION  OF  TO-DAY. 

master  the  others.  The  migrating  instinct  is 
stronger  among  birds  than  their  maternal  instinct, 
for  they  will  leave  their  young  to  perish  when  the 
migrating  time  appears.  Now  if  these  instincts  are 
transmitted  from  one  generation  to  another,  it  is 
easy  to  understand  their  preservation  and  develop- 
ment. Evidently  those  animals  with  instincts  best 
calculated  to  preserve  them  will  be  the  ones  to 
survive  the  struggle  for  existence,  while  those  which 
have  deleterious  instincts  will  be  destroyed.  By 
natural  selection,  therefore,  those  animals  whose 
strongest  instincts  are  best  calculated  for  the  good 
of  the  individual  will  continue  to  exist,  while  others 
will  disappear.  Further,  turning  to  the  instincts  of 
man,  the  instincts  which  developing  man  possessed 
will  be  assisted  by  his  intelligence.  He  will  be  able 
partially  to  understand  the  results  of  his  customs 
and  habits.  He  will  slowly  learn  to  follow  lines  of 
conduct  which  he  finds  best  adapted  for  the  preser- 
vation of  his  life,  and  will,  moreover,  soon  discover 
what  gives  him  the  most  pleasure.  Such  habits  will 
be  repeated  and  handed  down  from  generation  to 
generation,  until  they  finally  become  firmly  fixed  in 
the  race  as  inherited  habits  or  instincts.  Such 
instincts  become  the  moral  sense. 

But  this  is  not  reaching  the  bottom  of  the  matter, 
even  if  it  be  granted  for  a  moment  that  such 
instincts  can  become  a  moral  sense.  They  would 
make  duty  and  pleasure  the  same  thing,  or  at  all 
events  would  make  man's  duty  to  preserve  his  own 
life  his  only  duty.  But  every  one  realizes  that  many 
acts  which  we  feel  an  obligation  to  perform  are  not 


THE  MORAL   SENSE.  323 

only  productive  of  no  pleasure  (except  the  pleasure 
of  feeling  that  we  do  right),  but  they  sometimes  in- 
duce lasting  misfortune  or  even  death.  A  person 
who  possesses  a  fortune  which  belongs  to  another 
and  restores  it  to  the  rightful  owner,  performs  an 
act  which  every  one  will  consider  right,  even  though 
he  entail  privation  and  suffering  on  himself  and 
family  for  years.  No  one  questions  the  moral 
Tightness  of  the  sacrifices  of  martyrs.  Such  acts  as 
these,  of  which  there  are  thousands,  do  not  come 
under  the  explanation  given  above,  for  they  neither 
produce  pleasure  nor  preserve  life.  Most  of  our 
duties  are  indeed  sacrifices.  A  theory  of  develop- 
ment of  the  moral  nature  from  a  grade  of  the  brute 
must,  of  course,  include  this  class  of  actions,  which 
is  after  all  the  most  important.  Natural  selection 
of  instincts  would  lead  to  the  preservation  of  those 
individuals  who  best  take  care  of  themselves,  but  our 
moral  sense  teaches  us  to  care  for  the  weak  and  to 
help  each  other.  Our  ideas  of  duty,  and  particularly 
the  teachings  of  Christ,  have  largely  reversed  the 
law  of  self-preservation  which  is  universal  among 
animals.  Is  it  possible  for  Darwin  to  explain  the 
origin  of  this  feeling,  which  places  the  good  of 
others  before  our  own? 

The  origin  of  the  feeling  of  obligation  to  perform 
this  class  of  duties,  he  tells  us,  was  in  the  social  in- 
stincts of  primeval  man.  All  that  is  known  of 
primitive  man,  or  the  primates  from  which  he  is 
supposed  to  have  descended,  indicates  that  the 
earliest  men  lived,  as  they  do  to-day,  in  companies 
or  tribes.  In  these  social  communities  the  individ- 


324  EVOLUTION  OF  TO-DAY. 

uals  are  dependent  on  each  other,  as  we  always  find 
among  social  animals.  The  success  of  the  tribe  is 
the  success  of  the  individual,  and  the  defeat  of  the 
tribe  is  the  defeat  of  the  individual.  In  such  com- 
munities, therefore,  while  the  individual  may  have 
independent  pleasures,  he  cannot  have  an  indepen- 
dent existence.  Now,  as  we  can  judge  from 
savages,  these  tribes  have  always  been  in  conflict 
with  each  other,  and  in  these  contests  it  is  the 
strongest  tribe  and  not  the  strongest  individual, 
which  conquers  and  is  thus  able  to  leave  posterity. 
Natural  selection  will  have  the  effect  then  of 
strengthening  the  tribes  rather  than  the  individuals. 
Now,  strength  in  such  communities  consists  of 
mutual  dependence  and  union.  It  will  follow,  there- 
fore, that  those  tribes  of  primitive  men  (before  any 
idea  of  right  had  appeared)  which,  either  from  in- 
telligence or  blind  instinct,  chanced  to  have  the 
greatest  union  and  mutual  reliance,  would  be  the 
tribes  to  conquer  in  the  struggle  for  existence. 
Those  tribes  in  which  individual  happiness  was  not 
made  subservient  to  the  good  of  the  community 
would  be  exterminated.  History  is  full  of  illustra- 
tions of  this  fact.  In  this  way  the  good  of  the  com- 
munity becomes  a  superior  feeling  to  the  good  of 
self.  Habits  which  increased  this  union  would  be 
developed.  And  the  result  would  be  the  gradual 
development  of  various  social  instincts,  all  tending 
to  the  advantage  of  the  community,  though  often 
to  the  disadvantage  of  particular  individuals. 
Patriotism,  valor,  generosity,  sympathy,  justice,  etc., 
all  in  behalf  of  the  individuals  of  one's  own  tribe, 


THE  MORAL    SENSE.  325 

would  make  their  appearance.  For  the  tribes  with 
these  instincts  would  have  firmer  union  and  a  better 
chance  in  the  struggle  for  life.  They  would,  there- 
fore, be  more  flourishing,  and  would  gradually 
supersede  the  others.  Spencer  has  elaborately  dis- 
cussed this  subject,  and  has  ingeniously  tried  to 
prove  that  this  conception  will  explain  all  of  our 
beliefs  as  to  our  duty  to  others. 

Having  in  this  manner  accounted  for  the  origin  of 
inherited  habits,  all  tending  to  the  good  of  the  com- 
munity, and  thus  secondarily  to  the  good  of  the  in- 
dividual, one  more  step  is  taken,  and  man  is  sup- 
plied with  his  moral  nature.  These  habits  continue 
to  develop,  are  taught  to  children,  and  thus  handed 
down  from  generation  to  generation.  Finally,  by 
long-continued  inheritance,  they  come  to  occupy  a 
position  in  the  mind,  where  they  demand  obedience. 
"  Activities,  originally  proved  to  be  only  useful, 
were  inherited  as  traditional  instincts  by  the  off- 
spring, and  were  thus  freed  from  the  sensation  of 
the  useful  and  acted  as  authority."  They  eventually 
cease  to  be  impulses  or  acts  of  reason,  and  are  con- 
scientiously performed  as  acts  of  duty.  The  sense 
of  obligation  to  act  in  certain  ways,  and  the  idea  of 
right  and  wrong,  are  simply  the  results  of  long-con- 
tinued habit.  The  foundation  of  man's  duty  is  first 
the  preservation  of  the  tribe.  Then,  when  the  tribe 
becomes  absorbed  by  the  nation,  it  is  the  preserva- 
tion of  the  nation,  and  finally  it  will  be  the  preser- 
vation of  the  race. 

Such  is  the  development  theory  of  the  moral  na- 
ture, a  theory  which  amounts  in  brief  to  saying  that 


326  EVOLUTION  OF  TO-DAY. 

the  moral  sense  is  an  instinct  similar  in  nature  and 
origin  to  other  instincts.  Indeed,  the  explanation 
given  here  is  almost  exactly  the  same  that  is  given 
for  the  origin  of  instincts  in  general  among  animals, 
with  the  single  exception  that  intelligence  has 
played  a  larger  part.  If  the  theory  here  given  be 
compared  with  that  which  we  have  noticed  in  Chap- 
ter VI.,  explaining  the  origin  of  the  various  neuter 
castes  of  insects  with  their  instincts,  great  similarity 
will  be  seen.  Indeed,  the  development  of  the  in- 
stincts of  the  members  of  bee  communities  is,  so  far 
as  Darwin's  theory  goes,  the  same  as  that  of  the 
moral  nature  of  man.  It  is  difficult  to  see  how 
Darwin  can  make  any  distinction  between  the  in- 
stincts of  these  animals  and  the  moral  nature  of 
man.  It  is  just  as  much  the  duty  of  the  queen  bee 
to  kill  her  fertile  offspring,  as  it  is  for  man  to  give 
bread  to  the  hungry.  Each  act  is  the  result  of  an 
inherited  habit. 

It  is  hardly  nesessary  to  say  that  this  explanation 
of  Darwin's  is  rejected  by  a  large  number  of  think- 
ers. It  is  said  that  Darwin  has  misunderstood  the 
problem,  or  at  all  events  has  failed  to  account  for 
the  very  essence  of  the  whole  matter.  He  has  given 
interesting  suggestions  as  to  the  development  of 
codes  of  morals,  and  consequently  as  to  the  devel- 
opment of  the  moral  nature,  but  he  has  not  account- 
ed for  its  foundation,  z.  e.,  conscience.  He  has  de- 
scribed the  possible  origin  of  various  instincts,  and 
then  says  that  they  constitute  man's  moral  nature. 
But  is  it  possible  to  accept  the  conclusion  that  the 
moral  sense  is  simply  an  instinct  of  this  kind  ?  Most 


THE  MORAL   SENSE.  327 

people  would  unhesitatingly  answer  no.  A  person 
who  performs  an  act  because  he  feels  it  to  be  right, 
is  conscious  that  this  act  comes  under  a  category 
entirely  different  from  what  he  calls  instinct.  It  is 
an  instinct  for  a  child  to  suck,  but  no  one  calls  it  a 
moral  act.  Indeed,  none  of  the  actions  of  children 
are  considered  moral,  and  yet  they  have  instincts. 
We  feel  a  great  difference  between  these  two  classes 
of  actions,  though  it  may  be  difficult  to  define  it. 
The  one  is  followed  blindly ;  the  other  is  debated 
over,  and  not  un frequently  the  question  arises  as  to 
which  of  two  courses  is  right — a  question  impossible 
in  regard  to  instincts  proper.  This  difference  is  sel- 
dom appreciated  by  the  evolutionist,  though  it  is 
not  entirely  overlooked.  When  or  how  the  instincts 
which  are  at  the  base  of  the  moral  nature  became 
changed  in  their  nature,  they  do  not  clearly  indi- 
cate. But  in  some  way,  they  say,  long-continued 
repetition  from  generation  to  generation  caused 
them  to  become  regarded  as  authoritative,  and  thus 
to  constitute  duty. 

So  long  as  this  change  in  nature  is  not  explained, 
development  cannot  be  considered  as  meeting  the 
question  at  issue.  It  is  of  no  use  to  trace  the  de- 
velopment of  the  moral  nature  or  the  origin  of  social 
instincts,  unless  it  can  be  shown  that  they  are  the 
same.  Darwin  has  not  yet  shown  this,  and  few 
would  be  inclined  to  admit  it.  It  is  hardly  worth 
while  to  pursue  this  matter  further.  Enough  has 
been  said  to  indicate  the  position  of  the  two  sides. 
The  evolutionists  claim  that  conscience  is  simply  a 
modified  instinct,  that  the  moral  nature  has  arisen 


328  E  VOL  U  TION  OF  TO-DA  Y. 

from  social  instincts,  and  that  the  idea  of  right  is 
simply  a  generalization  of  a  class  of  actions  which 
have  been  found  to  be  productive  of  good.  But  on 
the  other  hand,  the  opponents  of  this  view  deny 
that  conscience  is  a  simple  instinct,  and  claim,  there- 
fore, that  Darwin  has  only  described  the  origin  of 
codes  of  morals  without  explaining  why  there  should 
be  such  morals.  Between  these  two  views  each 
must  decide  for  himself. 

General  Considerations. 

We  have  now  considered  the  chief  points  in  the 
Darwinian  argument  concerning  man.  It  consists 
entirely  in  showing  a  similarity  between  the  mental 
nature  of  men  and  animals.  The  arguments  found 
in  nature  for  believing  in  general  evolution  of  ani- 
mals, have  been  sufficient  to  convince  scientists  that 
evolution  is  true.  The  close  agreement  of  the 
human  body  with  that  of  other  vertebrates,  makes  it 
evident  that  if  we  accept  evolution  elsewhere  we 
must  also  do  so  here,  unless  some  valid  reasons  to 
the  contrary  appear.  But  if  we  consider  man  in  any 
other  relation  than  anatomically,  the  difference 
between  him  and  animals  is  enormous.  The  magni- 
tude of  this  difference  has,  therefore,  arisen  as  an 
obstacle  to  the  application  of  evolution  to  man. 
The  only  course  for  Darwin  and  his  followers  to 
pursue  is  to  show  that  this  difference  is  not  so  great 
as  it  seems ;  that  it  is  only  a  difference  in  degree. 
We  have  seen  the  method  by  which  this  is  attempt- 
ed ;  but  whether  the  attempt  has  been  successful,  is 
a  matter  of  dispute.  His  arguments  have  not  con- 


GENERAL   CONSIDERATION.  329 

vinced  his  opponents,  who  are  quite  numerous,  upon 
this  question.  On  the  other  hand,  his  followers 
claim  that  he  has  shown  the  animal  mind  to  be 
essentially  like  that  of  man,  and  this  is  all  that  can 
be  expected.  A  majority  of  scientists  would  hold 
this  position.  The  question,  therefore,  resolves 
itself  into  a  simple  one.  Are  the  characteristic 
qualities  of  the  human  mind,  such  as  the  power  of 
abstraction  with  its  accompanying  power  of  language, 
the  intuitions  of  causation,  time,  space,  etc.,  and 
its  unique  moral  sense, — are  these  qualities,  with  the 
powers  they  provide,  of  such  a  nature  that  they 
could  have  been  developed  from  the  mental  quali- 
ties of  animals  ?  To  this  question  each  man  must, 
after  careful  consideration,  give  his  own  answer. 

A  more  general  objection  to  the  views  of  the 
Darwinian  school,  than  any  of  the  above  is,  perhaps, 
the  most  important  of  all.  Even  if  it  be  granted 
that  a  development  such  as  supposed  might  have 
taken  place,  no  sufficient  cause  has  been  given  for 
the  remarkable  and  rapid  development  of  man.  All 
through  the  long  geological  ages  this  factor  of  intelli- 
gence remained  comparatively  undeveloped.  Some- 
what of  an  advance  there  was.  With  the  beginning 
of  the  tertiary  age,  as  we  have  seen,  there  was  an 
increase  in  the  size  of  the  brain.  This  increase, 
however,  in  most  cases,  amounted  to  little.  But  in 
man  it  was  so  great  and  so  rapid  that  in  a  compara- 
tively short  time  his  brain  became  twice  as  large  as 
that  of  other  animals.  His  intelligence  became  so 
great  that  the  difference  between  him  and  other 
animals  became  prodigious, — so  great  indeed,  that, 


3  3O  E  VOL  UTION  OF  TO-DA  Y. 

judging  by  results,  it  amounts  to  a  difference  greater 
than  any  other  distinction  found  among  animals. 
What  could  have  been  the  cause  of  this  remarkable 
development  in  this  one  case  alone  ?  As  an  explana- 
tion we  have  offered  to  us  natural  selection,  together 
with  the  suggestion  that  when  intelligence  had 
become  enough  advanced  to  create  language,  prog- 
ress would  be  very  rapid.  But  this  explanation 
appears  to  most  people  entirely  insufficient  to 
account  for  such  a  development,  even  supposing  the 
development  possible.  Natural  selection  seems  in- 
adequate anywhere,  and  it  certainly  seems  so  here. 
It  has  produced  this  result  in  no  other  case,  although 
the  intelligence  of  other  animals  than  primates  indi- 
cates that  there  was  equal  foundation  for  advance 
elsewhere.  It  must  assume  that  chance  produced 
the  beginning  of  intellectual  advance  in  the  human 
ancestors,  and  by  chance  Darwin  simply  means  an 
unknown  cause.  Here,  as  elsewhere,  even  if  evolu- 
tion be  a  fact,  its  explanation  is  yet  undiscovered. 

Another  point  must  be  mentioned  as  of  great  sig- 
nificance, though  we  might  not  find  all  scientists 
agreeing.  It  is,  however,  a  growing  conviction 
among  scientists  that  evolution  is  not  unlimited. 
There  has  been  in  all  ages  a  growth  from  the  general 
to  the  special.  An  unspecialized  form  is  capable  of 
very  great  development  in  numerous  directions,  but 
as  soon  as  it  becomes  highly  specialized  in  any  one, 
the  development  practically  ceases.  A  pocket-knife 
is  a  generalized  instrument,  and  may  be  used  for 
almost  any  purpose  from  cutting  down  trees  to 
carving  images.  It  is  capable  of  modification  in 


GENERAL   CONSIDERATION.  331 

any  direction  to  suit  these  purposes.  But  when  it 
reaches  high  specialization  in  any  one  direction,  it 
loses  its  power  to  develop  further.  The  graver's 
tool  can  cut  only  one  kind  of  line,  and  does  this  so 
well  that  further  advance  is  impossible.  And  so  in 
the  organic  world.  An  unspecialized  animal  is  capa- 
ble of  great  development  in  various  directions,  but 
after  it  has  become  specialized  its  advance  soon  be- 
comes limited  and  practically  ceases.  A  tree  cannot 
grow  forever.  After  reaching  a  certain  size  it  ceases 
to  develop  further  growth,  producing  only  leaves 
and  twigs.  Now,  it  follows  from  this  principle  that 
evolution  is  limited,  and  applying  the  principle  to 
man  it  will  become  probable,  not  only  that  he  is  the 
highest  animal  which  has  appeared,  but  also  the 
highest  that  will  appear.  The  last  generalized  fea- 
ture which  becomes  developed  is  the  mental  power. 
So  far  as  we  can  see,  this  is  the  highest  power; 
including  in  the  term  mental,  the  moral  powers 
as  well  as  the  intellectual.  The  mental  nature  was 
at  one  time  an  undeveloped  feature,  but  it  has  now 
become  developed,  and  the  specialization  of  this 
last  and  highest  quality  has  produced  man.  Now 
this  mental  nature  may  go  on  developing  and  be- 
coming more  specialized.  This  we  see  is  constantly 
taking  place.  But  the  result  can  never  be  any  thing 
but  man,  since  the  distinctive  characteristic  of  man 
is  the  possession  of  highly  developed  mental  powers. 
Man  stands  at  the  top  of  the  animal  kingdom,  not 
because  he  has  a  more  highly  developed  body  than 
other  animals,  for  this  is  only  partly  true.  It  is  be- 
cause his  distinctive  characteristic  is  the  great  develop- 


332  EVOLUTION  OF  TO-DA  Y, 

ment  of  the  highest  quality  which  animals  possess. 
With  this  understanding,  that  man  has  developed 
the  last  and  highest  realm  of  his  nature,  evolution  is 
seen  practically  to  end  with  him.  He  may  go  on 
becoming  more  and  more  specialized.  Other  ani- 
mals may  also  continue  to  produce  new  species. 
But  unless  there  is  some  other  and  higher  ungeneral- 
ized  feature  to  be  developed  in  the  future,  man 
stands  as  the  highest  order  of  beings  which  this 
world  will  produce.  Of  such  unspecialized  quality 
no  one  has  conceived.  Look  at  it  as  we  will,  the 
advent  of  man  must  be  regarded  as  the  development 
of  a  new  realm  in  nature.  Man  is  thus  radically 
separated  from  other  animals,  even  though  he  be 
derived  by  descent  from  them.  It  is  practically  im- 
material what  we  may  believe  man's  origin  to  have 
been,  his  distinction  from  other  animals  is  radical, 
and  we  may  accept  the  views  of  Darwin  and  Spencer 
without  altering  this  conclusion. 

General  Summary  of  this  and  the  Preceding  Chapters. 

Let  us  now  briefly  consider  what  may  be  regarded 
as  the  present  result  of  the  discussions  of  the  last 
twenty-five  years  upon  the  question  of  evolution. 
It  is  plain  that  the  different  theories  and  suggestions 
have  met  with  very  different  success  in  receiving 
support.  Some  have  been  so  well  authenticated  as 
to  be  almost  beyond  question  ;  some  have  been  left 
very  uncertain  ;  and  others  have  been  disproved. 

In  the  first  place,  the  candid  consideration  of  the 
subject  of  evolution — at  least  as  we  use  the  term, 
meaning  organic  evolution — has  shown  that  the  the- 


GENERAL   SUMMARY.  333 

ory  is  not,  as  was  at  first  thought,  an  alarming  blow 
at  theism.  It  is  simply  one  step  more  in  a  direc- 
tion in  which  thought  has  long  been  tending. 
In  the  early  ages  of  thought  every  phenome- 
non of  nature  was  looked  upon  as  the  direct  re- 
sult of  supernatural  agencies.  A  god  was  assumed 
to  account  for  every  unexplained  fact  of  nature. 
But  gradually  this  crude  conception  has  been  re- 
placed by  the  idea  of  a  single  God  governing  nature 
by  law.  Now  the  theory  of  evolution  is  sim- 
ply a  part  of  this  general  tendency,  assuming  that 
law  has  also  produced  the  present  organic  world. 
It  has  met  naturally  with  a  momentary  opposition, 
as  did  the  Copernican  theory,  or  the  theories  of 
geology.  But,  like  the  other  theories,  it  has  been 
found  to  demand  rather  than  do  away  with  the 
necessity  of  a  Creator.  It  is,  then,  a  purely  scientific 
theory  concerning  the  laws  of  the  organic  world. 

As  a  scientific  theory  it  is  now  generally  regarded. 
Scientists  claim  that  though  the  theory  has  not  been 
proved,  and  probably  never  will  be,  it  has  been  ren- 
dered so  probable  that  it  is  almost  beyond  the 
reach  of  question.  Every  possible  source  of  evi- 
dence which  has  promised  results  has  been  studied. 
The  effects  of  domestication  and  the  changes  of 
conditions  in  wild  animals  have  been  noted.  The 
results  here  have  proved  that  species  are  not  rigidly 
fixed,  but  are  subject  to  a  very  great  amount  of 
variation..  It  has  been  proved  that  the  differences 
between  the  varieties  thus  arising  may  be  greater 
than  that  between  species,  except  in  the  single 
character  of  sterility  ;  and  for  this  exception  an  ex- 


334  EVOLUTION  OF  TO-DAY. 

planation  partly  satisfactory  has  been  offered.  The 
classification  of  animals  and  the  relation  of  species 
to  each  other  have  revealed  a  bond  uniting  the 
organic  world  into  a  unit.  They  have  proved  that 
there  has  been  some  connection  between  all  organ- 
isms, and  the  assumption  that  this  bond  of  connec- 
tion is  heredity  has  been  found  to  meet  the  require- 
ments of  the  case.  The  order  of  appearance  of 
animals  in  the  past  has  further  testified  to  this  as- 
sumption, since  they  have  been  found  to  appear  in 
the  order  which  the  theory  would  expect.  Although 
the  sudden  appearance  of  a  highly  diversified  fauna 
in  the  earliest  rocks  which  give  us  any  record  is 
somewhat  of  a  surprise,  yet  the  evidence  elsewhere 
has  been  conclusive.  Still  more  forcibly  has  this 
same  uniting  bond  been  proved  by  embryology. 
Here,  too,  in  a  marvellous  manner  has  the  evidence 
pointed  to  heredity  as  this  bond.  Until  to-day  the 
subject  of  classification,  paleontology,  embryology, 
and  genetic  descent  are  so  intimately  combined  that 
it  is  no  longer  possible  to  separate  them.  Finally, 
the  geographical  distribution  of  animals  has  offered 
its  evidence,  and  in  some  cases,  /.  e.,  oceanic 
islands,  has  presented  a  practical  demonstration 
that  new  species  can  arise  from  old  ones. 

All  of  this  evidence  together  forms  an  argument 
that  no  one  who  has  carefully  studied  the  matter 
has  been  inclined  to  deny.  It  is  true  that  all  of  the 
difficulties  have  not  yet  been  cleared  away,  and  that 
some  of  them  seem  to  indicate  that  there  are  other 
laws  of  life  not  comprised  in  the  theory  of  evolu- 
tion. Beyond  difficulties  of  detail,  which  of  course 


GENERAL   SUMMARY.  335 

can  probably  never  be  fully  explained,  the  objec- 
tions to  evolution  in  general  are  very  few,  and  are 
gradually  disappearing.  The  conclusion  of  science 
is,  therefore,  that  organic  evolution  is  a  fact,  and  we 
may  regard  it  as  one  of  the  theories  of  science 
which  is  to  remain  as  a  foundation  for  future  advance. 
When  we  next  ask  as  to  the  limits  of  evolution, 
we  reach  a  question  whose  answer  is  much  less  cer- 
tain. Recognizing  that  the  essence  of  the  theory 
of  evolution  is  the  substitution  of  natural  law  for 
miracle,  it  is  evident  that  if  applied  to  its  fullest  ex- 
tent it  would  include  the  whole  universe.  Conse- 
quently we  find  Spencer  and  others  do  carry  the 
principle  as  far  as  it  is  logically  possible  for  them  to 
do,  and  comprise  within  its  far-reaching  influence 
the  development  of  every  thing  from  the  nebula. 
But  even  this  extreme  reaches  no  satisfactory  stop- 
ping-place, for  the  nebula  could  not  have  been 
evolved.  Indeed,  a  logically  complete  theory  is  im- 
possible. Recognizing  this,  most  scientists  prefer 
to  leave  out  of  consideration  the  question  of  specu- 
lation, and  confine  the  term  evolution  to  the  realm 
where  evidence  demands  it.  Now  a  break  is  found 
at  the  beginning  of  life.  Most  scientists  would 
doubtless  be  very  glad  to  be  able  to  prove  that  life 
can  originate  from  inorganic  matter,  but  they  do  not 
claim  to  have  any  evidence  that  it  can  do  so  ;  nor, 
indeed,  have  they  any  evidence,  except  the  logic  of 
the  evolutionary  theory,  that  it  ever  has  done  so. 
This  matter  is  therefore  generally  omitted  from  the 
discussion,  as  at  present  impossible  either  of  proof 
or  disproof. 


336  EVOLUTION  OF  TO-DAY. 

Another  break  is  found,  according  to  the  opinion 
of  some,  at  the  other  end  of  the  series.  Man  is  by 
them  exempted  wholly  or  in  part  from  the  general 
law  of  evolution.  This  break  is  a  more  debatable 
one  than  that  at  the  origin  of  life.  The  close  rela- 
tion of  man  to  other  vertebrates  anatomically, 
renders  it  almost  beyond  question  that  so  far 
as  his  body  is  concerned,  he  has  been  subject 
to  the  same  law  which  has  regulated  other  ani- 
mals. But  his  peculiar  mental  powers  made  him 
something  different.  Darwin,  and  many  followers, 
do  not,  however,  look  upon  this  as  a  break,  but  sim 
ply  a  difference  in  degrees  of  the  development  of 
mental  powers.  They  claim  to  find  the  same  men- 
tal powers  in  animals  which  are  found  in  man,  and 
would  say  that  when  the  ancestors  of  man  reached 
a  certain  stage  in  their  development,  their  intellect 
began  to  grow.  The  start  was  due  to  accident,  but, 
once  started,  natural  selection  rapidly  increased  the 
growth,  until,  in  a  comparatively  short  time,  man, 
with  all  of  his  mental  powers,  was  the  result. 
Others  would  say  that  while  this  difference  is  only 
one  of  degree,  the  degree  of  difference  is  enormous ; 
too  great,  indeed,  for  Darwin's  theory.  While, 
then,  it  is  possible  that  man  has  arisen  by  develop- 
ment, no  sufficient  cause  has  been  discovered  for 
the  sudden  rapid  growth  of  mental  power  in  man. 
They  would  say  that  "  some  unknown  cause  accel- 
erated development,"  meaning  by  this  unknown  the 
Creator.  Others  deny  the  possibility  of  man's 
origin  by  development,  considering  his  powers  as 
new  in  kind.  They  would  say  that  at  the  appear- 


GENERAL   SUMMARY.  337 

ance  of  man  new  qualities  were  given  him  by  his 
Creator.  But  all  agree  that  man  is  radically  set 
apart  from  the  rest  of  the  animal  kingdom  by  his 
mental  nature.  While  anatomically  he  is  an  ape, 
mentally  he  is  not  only  a  new  order  of  being,  but 
probably  also  the  highest  and  the  last. 

When,  finally,  we  come  to  ask  what  has  been  the 
cause  or  causes  producing  evolution,  we  find  a  great 
many  answers.  No  two  scientists,  perhaps,  fully 
agree.  The  theory  of  natural  selection,  advanced  at 
the  outset  by  Darwin,  has  proved  to  be  an  import- 
ant factor,  but  inadequate  to  reach  many  classes  of 
facts  which  require  explanation.  Not  only  is  it 
open  to  difficulty,  but  it  has  become  evident  that  at 
best  it  is  only  secondary.  The  selection  of  the  fit- 
test forms  can  only  come  after  their  appearance, 
and  the  origin  of  variations  has  demanded  more 
and  more  attention.  Darwin's  explanation  hardly 
touched  this  question,  or,  at  all  events,  only  ac- 
counted for  indefinite,  irregular  variations,  which 
have  been  plainly  shown  to  be  insufficient.  A  num- 
ber of  other  theories  have  attempted  to  avoid  the 
difficulties  which  natural  selection  meets.  But  none 
of  them  are  in  themselves  really  satisfactory.  Some 
are  more  difficult  to  understand  than  the  facts  they 
try  to  explain ;  some  do  not  meet  the  facts  ;  some 
would,  if  granted,  explain  the  facts,  but  have  little 
evidence  in  their  favor.  Yet  all  of  them,  probably, 
express  some  truth.  The  fact  is  that  the  organic 
world  is  not  simple,  and  there  are  a  great  many  fac- 
tors at  work.  The  origin  of  species  has  been  the 
result  of  not  one  but  many  causes.  Some  of  them 


338  EVOLUTION  OF  TO-DAY. 

have  been  discovered,  and  probably  others  remain 
yet  unthpught  of.  The  reproduction  of  organic 
beings  is  the  result  of  two  somewhat  contradictory 
laws,  Heredity  and  Variation.  In  accordance  with 
the  first,  species  tend  to  produce  offspring  precisely 
like  themselves.  In  accordance  with  the  second, 
they  tend  to  produce  offspring  differing  from  them- 
selves. These  two  laws,  and  the  forces  governing 
them,  must  be  the  factors  which  have  produced 
whatsoever  evolution  there  has  been.  Naturalists 
are  now  at  work  endeavoring  to  reach  a  better  un- 
derstanding of  these  laws,  and  out  of  their  work  we 
may  hope  for  further  knowledge.  At  present,  then, 
while  it  is  well  to  admit  with  the  scientist  that  or- 
ganic evolution  is  probably  true,  and  that  it  may  or 
may  not  include  man,  it  is  also  evident  that  the 
complete  explanation  of  the  theory  has  not  been 
reached.  Above  all,  the  investigations  have  not 
brought  scientists  much  nearer  to  the  real  signifi- 
cance of  life  itself,  which,  like  all  other  first  princi- 
ples, becomes  the  more  inexplicable  the  more  it  is 
studied. 


INDEX. 


Abbreviation  of  embryological 
history,  131 

Aborted  organs,  80 

Absence  of  generalized  forms,  99 

Abstract  ideas,  311 

Accelerated  development,  265 

Activity  as  a  modifying  cause, 
262 

Agassiz  and  classification,  55 

Agassiz,  A.,  work  on  embryol- 
ogy, 124 

Age  of  the  world,  97,  215 

Air-bladder  of  fishes  and  lungs, 
83,  84 

American  birds,  change  in  color, 
25 

Amoeba,  270 

Amphioxus,  64 

Ancon  sheep,  226,  257 

Annelid  development,  129 

Apes,  188,  291,  310 

Application  of  embryology  to 
whole  animal  kingdom,  147 

Archeopteryx,  no 

Arctic  and  Alpine  flora,  183,  186 

Are  species  stable  ?  32 

Artemia,  26,  33 

Ascidians,  64 

Australia,  172,  175,  184,  198 


B 


Barriers  limiting  specific  distribu- 
tion, 183 
Bats,  1991,  34 


Beginnings  of  life,  7 
Beginnings  of  organs,  226 
Bermudas,  192 
Bermuda  lizard,  199 
Birds  of  paradise,  181 
Blind  cave  animals,  274 
Boa-constrictor       crossing       the 

ocean,  194 
Bobolink,  195 
Brain  of  mammals,  development 

of,  114 

Breaks  in  continuity,  7,  8,  9 
Broca,  on  fertility  of  human  race, 

35 
Brooks'  theory  of  heredity,  277 


Camels,  distribution  of,  181 

Carnivora,  66 

Causation,  313 

Cetacea,  66 

Classification,  55  ;  significance 
of,  53 

Colorado  potato  beetle,  166 

Comparison  of  arguments  of  Ag- 
assiz and  Darwin,  57 

Composgnathus,  no 

Condylarthra,  no 

Congenital  variations,  274 

Connecting  links,  63  ;  among  fos- 
sils, 65,  91,  107  ;  geological 
position  of,  ill 

Consciousness,  266,  308 

Conscience,  315 

Contradiction  between  embryo- 
logical  histories,  127 


339 


340 


E  VOL  UTION  OF  TO-DA  Y. 


Cope  on  consciousness,  266 
Correlated  variations,  221 
Crosses,  37  ;  eliminating  charac- 
teristics, 224 
Crustacea,  73,  112 
Cuvier,  12,  55 


Dakota  formation,  116 

Darwinism,  208 

Datura  tatula,  257 

Dicotyledons  in  cretaceous,  116 

Dipnoi,  84 

Direct  and  indirect  development, 

135 

Dispersal,  means  of,  184 
Distinction    between    man    and 

brute,    329 
Distribution,  and  climate,  166  ;  of 

families,  181  ;  of  orders,  182  ; 

of  species,  179 
Diversity  of  Silurian  life,  103 
Dogs,  35,  38,  41,  302,  304,  312, 

319 
Duke  of  Argyle,  300,  320 


Echinoderms  of  Silurian,  100 
Edentates,  171,  188 
Effort  a  modifying  cause,  264 
Elephants,  breeding  of,  42 
Embryology,  a  repetition  of  past 
history,  122  ;  an  assistance  in 
classification,   139  ;    compared 
with  hypothetical  history,  126  ; 
history  in  general,  155 
Emotions,  304 
Eozoan  Canadense,  94,  96 
Evolution,    not    Darwinism,    9, 

208  ;  and  theology,  13 
Extraordinary  births,  255 
Eye  in  vertebrates  and  mollusKS, 
232 


Falsification  of  embryological  his- 
tory, 134 


Fertility  of,  hybrids,37  ;  varieties, 

34 

First  appearance  of  life,  94 
Food-yolk,  effects  of,  129 
Fresh-water      animals,     distribu- 
tion,   183, 184 
Frog  of  Guadaloupe,  132 
Frogs  on  islands,  193 


Galapagos  islands,  194 
Galaxias  attenuatus,  187 
Gastrula,  156 
Gemmules,  276,  278 
General  summary,  232 
Glacial   age,    effect   on   distribu- 
tion.   174 
Greenland  whale,  227 

H 

Haeckel's,  history  of  man,  149  ; 
theory  of  heredity,  275 

Heredity,  213,  269 

Homology  and  analogy,  70  ;  ex- 
planation, 71  ;  between  types, 
62  ;  in  young  stages,  62 

Horse,  31,  39,  49,  109,  167,  173, 
231  ;  history  of,  109 

Human  race,  a  possible  case  of 
sterility,  35 

Huxley  and  comparative  anat- 
omy, 53 

Hybrids,  38 

Hypothetical  stages,  148 

Hyracoidea,  66 


Imperfection  of  paleontology,  90 

Importance  of  embryology,  I2O 

Impossibility  of  a  complete  evo- 
lution theory,  6 

Incompleteness  of  Darwinism, 
213 

Individual  variation,  26 

Indirect  evidence  of  immuta- 
bility, 45 

Inherent  tendency  to  vary,  29, 
213 


INDEX. 


341 


Inheritance  of  acquired  varia- 
tions, 270,  273 

Insectivora,  181 

Instinct  and  moral  sense,  320, 
327 

Intelligence,  294,  296,  299 

Internal, factors  in  evolution, 252  ; 
laws  of  variation,  29,  252 

Islands  once  connected  with 
mainland,  198 

Isolation,  effect  of,  190,  247 

Isthmus  of  Panama,  183,  184 


J 


Sager's  theory  of  heredity,  276 
ay,  179,  180 


Knowledge  of  tools,  fire,  etc.,  305 
L 

Lamarck,  n,  262 
Language,  306 
Larval  life,  effect  of,  145 
Laws  of  distribution,  168 
Life  in  Silurian,  94 
Limits  of  variation,  31 
Lingula,  106 

M 

Magpie,  180 

Mammals  on  islands,  193 
Man  as  a  fossil,  292 
Man  the  highest  animal,  331 
Man's  influence  on  distribution, 
Man's  physical  nature,  290 
Marsh-tit,  179 
Marsupials,  172,  178,  252 
Meehan,  250 

Migration  theory  of  Wagner,  247 
Mimicry,   235 
Minute  steps,  226 
Missing  link,  65 
Mivart,  255,  320 
Mole,  180 

Monkeys,  New  and  Old  World, 
171,  177,  178 


Moral,  nature,  314  ;  sense,  317, 
320 ;  sense  in  animals,  318 ; 
sense  as  explained  by  Darwin, 
320 

Mutability  of  species,  22 


Nageli,  inherent  tendency  to 
vary  theory,  253 

Narrow  straits  as  barriers,  199 

Nascent  organs,  82 

Natural  selection,  208 ;  origi- 
nates nothing,  213  ;  still  ac- 
cepted as  sufficient  by  some, 
246 

Negro,  310 

Neo-Lamarckianism,  29,  262 

Notochord,  133 

Number  of  types,  60 

O 

Oceanic  islands,  189 
Odontornithes,  no 
Ontogenetic  descent,  78 
Origin  of  variations,  251 
Ovum,  division  of,  272 


Paleobotany,  115 

Pangenesis,  theory  of,  276 

Parallel  between  embryology  and 
paleontology,  123 

Peacock,  258 

Pigeon,  24,  26,  34,  46,  48,  191, 
247 

Planorbis,  46 

Potto,  230 

Power  to  improve,  309 

Presilurian  times,  96 

Prevalence  of  the  evolution  the- 
ory, 1 8 

Primates,  292,  296 

Proboscidea,  66 

Prophetic  organs,  82 

Protista,  67 

Pug-dog,  26 


342 


EVOLUTION  OF  TO-DAY. 


R 


Race-horses,  31 

Rats  on  the  island  of  Formosa,  25 

Reciprocal  crosses,  39 

Relation  of  the  present  animals 

to  the  past,  171 
Religion,  314 
Return  to  the  original  condition 

of  domestic  animals  becoming 

feral,  43 
Revelation,  17 
Reversions,  47 

Rhyncophora  of  St.  Helena,  197 
Ritta,  I  So 
Rodents,  66 
Romanes,  302,  303,  320 
Rudimentary  organs,  78,  267,  291 


Schmankewitsch,  experiments  on 
artemia,  26 

Scorpions,  95 

Sea-urchins,  fossils,  112 

Separation  of  the  sub-kingdoms 
from  gastrula,  158 

Serial  homology,  72 

Sexual  selection,  210 

Significance  of  the  parallel  be- 
tween embryology  and  paleon- 
tology, 140 

Silurian  animals  all  marine,  107 

Similarity  of  independently  ac- 
quired organs,  231 

Sirenia,  66 

Slowness  of  modification  by  natu- 
ral selection,  215 

Specialized  fauna  of  the  Silurian, 
loo 

Species  not  definable,  32 

Spencer,  5,  15,  73,  315 

Spontaneous  generation,  4,  7 

Steinheim  Lake  deposit,  46 

Sterile  insects,  237 


Sterility,  a  variable  quantity,  39  ; 

explanation  of,  40 
St.  Helena,  196 
Summary  of  all  the  evidence,  20, 

203,  232 

Supernatural,  315 
Synthetic  types  few  in  number  of 

individuals,  102 


Tapir,  188 

Teeth  of  ungulates,  268 

Theistic  evolution,  17 

Thrush-tit,  180 

Tortoises  of  the  Galapagos 
islands,  195 

Transitional  varieties  wanting  in 
most  cases,  217 

Tree- like  arrangement  of  rela- 
tions, 58 

Trochosphere  stage  of  mollusks 
and  worms,  62 

Tsetze  fly,  166 

Tyndall  and  spontaneous  genera- 
tion, 7 

Types,  number  of,  60 


Ungulates,  66,  268 

Unity  of  the  organic  world,  58 

Unspecialized,    doctrine  of   the, 
330 

Use  and  effort,  262,  263 

Uselessness  of  many  characteris- 
tics, 219 

W 

Wagner,  theory  of  migration,  247 
Weissmann,  theory  of  heredity 

269 

Zoological  regions,  176 


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